Just to clarify for the people that are as confused and clumsy as I am. This diskimage.device manifests something that you can call "crapshoot behaviour" - so it either works fine sometimes and sometimes it just crashes your entire system - particularly it seems to dislike mounting simple Amiga ADF images (nothing fancy, like NRG or some such). I have removed it from my Amiga and replaced it with:
which, granted, is a 11 years older and does not support that many image formats, however it does not arbitrarily crash the system.
In case the developer will update the library, I will switch back. For now, you can give the Thore Böckelmann version (link above) a try since it does not have issues with mounting ADFs.