1.11.5 broken png thumbnail transparency

[deil]

XnView: MP 1.11.5 64 bit
OS: Windows 10Pro 22H2 64bit

The previews for some png files have white areas in place of the actual picture. I attached examples of such png files.
If you click "rebuild thumbnails", all white pixels are gone, but once you restart XnView, they're back.
If you disable "Use transparency grid", instead of white it will be some sort of grey (maybe it's because my theme has a grey background). It's still the wrong color, clicking "rebuild thumbnails" make it obvious.
This bug wasn't present in 1.11.2 iirc, don't know about 1.11.3 and 1.11.4.
To me it looks like the bug is in how the XnView loads existing thumbnails from the db.

Effect: When you open the XnView, previews for some png files looks like they have a lot of white pixels.

To reproduce:
1. Fresh install 1.11.5
2. Disable "Create high quality thumbnail" in settings
3. Make sure "Use transparency grid" is enabled (makes bug much more noticeable when using a theme with grey background)
4. Navigate to the folder with the png files (I attached few in a zip file) so the XnView would create a preview for them.
5. Restart Xnview and look at these previews.
Optionally:
6. Click "View"->"Rebuild Thumbnails", the thumbnails look fixed.
7. Restart Xnview and look at previews, they're broken again.

Actual behaviour (bug): White pixels in thumbnail.

Expected behaviour: Properly built thumbnail, without white pixels replacing actual colors.

1. 'use transparency grid' enabled.png

2. 'use transparency grid' disabled.png

3. proper thumbnails.png

[user0]

same
1.11.5 - browser - thumbnails - png - shows first index as transparent