This is related to a bug report
I made, that is apparently not actually a bug.
The situation :
I always store the album cover as a separate file in the album folder. Depending on the case, the file will either be named cover.png if I had a lossless source or cover.jpg otherwise.
The problem :
As it is, MusicBee systematically converts my PNG files to JPG whenever I edit the tags of the album. This creates duplicate covers (ie both cover.PNG and cover.JPG are present), which wastes space and feels messy.
The solution :
In the following dialog, allow the user to ignore file format altogether in the cover storage options (for example using cover.*, whereby MusicBee would auto-detect the file). Only the name would matter and not whether it's JPG or PNG or whatever else.
I believe implementing that would also fit with the other cover options that allow a lot of liberty in the naming and format of the cover (.*).