How to really delete maps files *.mca?

Due to storage space problems I decided to temporarily delete all Maps in MapFactor Navigator -->Maps Manager under Android 7.
The App itself is kept.

Afterwards I run a treespace diagnostic over my SmartPhone with Android 7 and found out that all map files *.mca are still existing.

See this snapshot:

https://s7.postimg.cc/3weu5onsb/deleted_maps_still_exists_for_Mapfactor.png

Why?

I think this is a bug

How do I really get rid of the map files?

Peter