1.3.1: thumb database size-limited and no space counting

[Fufufufu]

XnView: MP 1.3.1- 64 bit
OS: Windows 10 64bit

a) The Thumb.db file is stuck at 928 MByte size and will not grow even if I feed Xnview with more images.
b) in tools / settings / catalogue I do see the folderpaths of images where I generated thumbnails. And it does show the correct file number counts. But the volume sizes in Bytes is listed as zero for any but 4 of my folders. And the sum of those four is 200 MB.

Effect: Xnview does generate new thumbnails every time I visit a directory, close the program and restart it.

Hint: My scenario has > 10.000 relatively small source JPGs and I do generate relatively big thumbs at 600x600 px.

[masterjp]

Did you try the 'optimize' Button to shrink the database?
It can remove unused thumbnails of deleted files.
In some cases it shrinks the database to a smaller filesize.