I have been following the thread at HA.org about (cover) images in APEv2 tags with intereset and I'm happy that Mp3Tag now supports them. Although I'm confused about why there have to be two ways of storing images in APEv2 now.
Anyway, I found a bug in the 2.38b:
I noticed that when I add more than one image to an APEv2 tag (Alt-T, add image, add image, ... , "Ok"), I get the message "!BAD APE2" from %_tag%.
If I add them one by one (Alt-T, add image, "Ok", Alt-T, add image, "Ok",...), everything is ok.