Report on defect thumbnailing

[soulky]

For a reason I cannot find out, thumbnailing needs several passes. Something is seriously defect with the thumbnailing function.
It "works" like this:
1. Thumbnailing starts. Files get thumbnailed in an accident order. Thumbnailing whole folder is enabled.
2. Progress bar goes to 100%, thumbnailing finished.
3. Only a few thumbnails are visible. Number of thumbnailed images in setting is around 300. (From 20000 files)
4. Close XnviewMp, start it again.
5. Thumbnailing starts again. After a while progress bar is at 100%. But same result as before. Now number of thumbnailed files is around 800.
6. Close XnwiewMP again. Start it again.
7. Thumbnailing starts again. You can see that files that have not been thumbnailed before, getting thumbnails now.
8. But same as before, progress bar goes to 100%. Thumbnailing stops. Number of thumbnailed files in settings: 2000.
And so on and so on. With every pass, more thumbnails getting created. But every pass takes HOURS to complete. So there is a real defect in the software. Harddrive is working all the time and you can hear it is accessing files one by one. But it is not thumbnailing them.
Something is seriously not working the way it should.