There seems to be a discrepancy for generating thumbnails on folders containing a folder.jpg and trying to modify their size via Set THUMBNAILSIZE as opposed to via Preferences.
Testbed: We have 6 wallpapers at 2560x1600 resolution added in 6 numbered folders and named folder.jpg
Step 1:
Setting the thumbnail size in Prefs > Thumbnails > Appearance to the same aspect ratio of the folder.jpg images results in this:
Step 2:
Setting it to 512x512 in preferences results in this:
Step 3:
So far so good. However when we use Set THUMBNAILSIZE 512,340 to set the wide view and save vertical space we get this.
So either the setting via Set THUMBNAILSIZE does not have the same effect as preferences.
Or there is some strange caching going on, which even Go REFRESHTHUMBS can't do anything about.
I've experienced this behavior in the past with CBZ and CBR archives and their covers but those seem to work fine lately.
On a side note - the ability to set thumbnail size or at least aspect ratio on a per-folder-format basis would be immensely helpful. Both content-type formats and wildcard ones would benefit from that.