Simple search for description content: Inconsistent search behaviour?

[hofmannc]

Testserver: qa imeji
Browser: ff
Version: 4.5.3 - build date 2019-05-28 09:30:51
User: admin

Why do I find two collections (corretly) if I search for e.g. "Frashëri" or "Shqipëria" or "Literat" , but nothing if I search for e.g. "Aktivisten" or "albanischen" or "Nationalbewegung" ?

[haarli]

The text contains a lot of non-unicode characters, which are invisible. Words with those characters cannot be found.