iCal-Import from .ics-file with splitted-up categories

Hi there everybody,
i would like to import outlook-events via an .ics-file (once per day automatically).
The import-mechanism in Plone 5 works good so far,
but the event.item 'categories' is beeing splitted: for example "Homepage" --> 'H','o','m',.... .

I tried to fix this in /Plone/buildout-cache/eggs/plone.app.event-2.0.12-py2.7.egg/plone/app/event/ical/importer.py, but the splitting is done elsewhere, maybe there:

Maybe somebody is familiar with this topic or has solved this problem already.

Thank you in advance,

Which version of Plone are you using? What other add-ons do you have in the buildout?

In Plone 5.0.7 the categories on events work fine for me: