Mockup: select2 inside modal duplicate widget (bug?)

I'm working on an application on Plone 5.0.x, trying both shipped mockup and 2.4.1, and in both cases, I get a duplicate select2 widget when trying to use the pattern (reproducable using mockup examples) inside a modal, with one of the widgets correctly configured, the other not, with traceback on page load:

patterns.pat.select2: Failed while initializing 'select2' pattern. query function not defined for Select2 s2id_input-autofind  plone-compiled.min.js:1:17468
	output http://localhost:28181/hello1/++plone++static/++unique++2015-02-16%2000%3A00%3A00/plone-compiled.min.js:1:17468
	log http://localhost:28181/hello1/++plone++static/++unique++2015-02-16%2000%3A00%3A00/plone-compiled.min.js:1:18196
	error http://localhost:28181/hello1/++plone++static/++unique++2015-02-16%2000%3A00%3A00/plone-compiled.min.js:1:18373
	f http://localhost:28181/hello1/++plone++static/++unique++2015-02-16%2000%3A00%3A00/plone-compiled.min.js:2:3070
	initPattern http://localhost:28181/hello1/++plone++static/++unique++2015-02-16%2000%3A00%3A00/plone-compiled.min.js:2:919
	D http://localhost:28181/hello1/++plone++static/++unique++2015-02-16%2000%3A00%3A00/plone-compiled.min.js:1:7255
	c http://localhost:28181/hello1/++plone++static/++unique++2015-02-16%2000%3A00%3A00/plone-compiled.min.js:1:7778
	scan/< http://localhost:28181/hello1/++plone++static/++unique++2015-02-16%2000%3A00%3A00/plone-compiled.min.js:2:1541
	scan http://localhost:28181/hello1/++plone++static/++unique++2015-02-16%2000%3A00%3A00/plone-compiled.min.js:2:1503
	_show http://localhost:28181/hello1/++plone++static/++unique++2015-02-16%2000%3A00%3A00/plone-compiled.min.js:7:21519
	createTargetModal http://localhost:28181/hello1/++plone++static/++unique++2015-02-16%2000%3A00%3A00/plone-compiled.min.js:7:18428
	show http://localhost:28181/hello1/++plone++static/++unique++2015-02-16%2000%3A00%3A00/plone-compiled.min.js:7:20377
	init/< http://localhost:28181/hello1/++plone++static/++unique++2015-02-16%2000%3A00%3A00/plone-compiled.min.js:7:17788
	dispatch http://localhost:28181/hello1/++plone++static/components/jquery/dist/jquery.min.js:4:8497
	b.dispatch http://localhost:28181/hello1/++plone++static/++unique++2015-02-16%2000%3A00%3A00/plone-compiled.min.js:4:6149
	add/r.handle http://localhost:28181/hello1/++plone++static/components/jquery/dist/jquery.min.js:4:5235
	(Async: EventListener.handleEvent)
	add http://localhost:28181/hello1/++plone++static/components/jquery/dist/jquery.min.js:4:5723
	on/< http://localhost:28181/hello1/++plone++static/components/jquery/dist/jquery.min.js:4:15011
	each http://localhost:28181/hello1/++plone++static/components/jquery/dist/jquery.min.js:2:2973
	each http://localhost:28181/hello1/++plone++static/components/jquery/dist/jquery.min.js:2:833
	on http://localhost:28181/hello1/++plone++static/components/jquery/dist/jquery.min.js:4:14990
	init http://localhost:28181/hello1/++plone++static/++unique++2015-02-16%2000%3A00%3A00/plone-compiled.min.js:7:17720
	g http://localhost:28181/hello1/++plone++static/++unique++2015-02-16%2000%3A00%3A00/plone-compiled.min.js:2:3241
	g.extend/d< http://localhost:28181/hello1/++plone++static/++unique++2015-02-16%2000%3A00%3A00/plone-compiled.min.js:2:3645
	f http://localhost:28181/hello1/++plone++static/++unique++2015-02-16%2000%3A00%3A00/plone-compiled.min.js:2:3036
	initPattern http://localhost:28181/hello1/++plone++static/++unique++2015-02-16%2000%3A00%3A00/plone-compiled.min.js:2:919
	D http://localhost:28181/hello1/++plone++static/++unique++2015-02-16%2000%3A00%3A00/plone-compiled.min.js:1:7255
	c http://localhost:28181/hello1/++plone++static/++unique++2015-02-16%2000%3A00%3A00/plone-compiled.min.js:1:7778
	scan/< http://localhost:28181/hello1/++plone++static/++unique++2015-02-16%2000%3A00%3A00/plone-compiled.min.js:2:1541
	scan http://localhost:28181/hello1/++plone++static/++unique++2015-02-16%2000%3A00%3A00/plone-compiled.min.js:2:1503
	init/< http://localhost:28181/hello1/++plone++static/++unique++2015-02-16%2000%3A00%3A00/plone-compiled.min.js:2:448
	j http://localhost:28181/hello1/++plone++static/components/jquery/dist/jquery.min.js:2:27304
	add http://localhost:28181/hello1/++plone++static/components/jquery/dist/jquery.min.js:2:27618
	m.fn.ready http://localhost:28181/hello1/++plone++static/components/jquery/dist/jquery.min.js:2:29706
	<anonymous> http://localhost:28181/hello1/++plone++static/++unique++2015-02-16%2000%3A00%3A00/plone-compiled.min.js:12:30878
	execCb http://localhost:28181/hello1/++plone++static/components/requirejs/require.js:1670:24
	check http://localhost:28181/hello1/++plone++static/components/requirejs/require.js:874:43
	enable http://localhost:28181/hello1/++plone++static/components/requirejs/require.js:1161:17
	init http://localhost:28181/hello1/++plone++static/components/requirejs/require.js:782:21
	localRequire/< http://localhost:28181/hello1/++plone++static/components/requirejs/require.js:1435:25
	(Async: setTimeout handler)
	req.nextTick< http://localhost:28181/hello1/++plone++static/components/requirejs/require.js:1775:9
	localRequire http://localhost:28181/hello1/++plone++static/components/requirejs/require.js:1424:21
	requirejs http://localhost:28181/hello1/++plone++static/components/requirejs/require.js:1757:16
	<anonymous> http://localhost:28181/hello1/++plone++static/++unique++2015-02-16%2000%3A00%3A00/plone-compiled.min.js:12:30320

Is there something subtle I am missing, or is this a new bug or known issue?

Sean