When selecting a group of WMA files (all in the same dir) and trying to apply a cover to them, the cover is not inserted in all the files. I tried to check whether there was a pattern that could explain which file ended up with the cover and which did not, but the behaviour seems random.
This problem happens when manually including a local JPEG, but also when importing the cover from a service like Amazon. In such a case the checkbox "Save image in tag" does the same thing and not all selected files end up with the image in their tag. It also occurs when creating a script that imports the covers from "folder.jpg" and applying it to a large batch of files.
Sometimes, even selecting a single WMA and trying to add a cover to it takes two or three tries before the cover is finally included.
In all these cases, the program indicates nonetheless that the modification is successful. I get no warning about file write access and do not consider that to be the culprit.
Other than that, the program does a fine job. Congrats!