Persistent dependency

I noticed since some days ago that every time I run buildout on buildout.coredev's 5.0 branch I get a warning about an unpinned egg:

persistent = 4.1.1

Isn't this one supposed to be avoided?

yes, this is the one to be avoided

It is from z3c.form. Luckily only a test dependency, that is why it didn't break any plone installation.

Background about not having persistent as a dependency:

The version of zodb3 we are using does still come with persistent included.
The earliest version of persistent as a package of its own already contains backward imcompatible changes that break in interesting ways.