This is a thing that has been happening to me for quite some time now, when I select 20+ or so files for tag removal, not all of them are removed. I have to sometimes repeat the process several times before all tags disappear.
This happens sometimes with even fewer files selected. I changed my whole PC in the meantime, so something related to that is not the case.
I’ve seen this sometimes (with older 2.4x builds) when files had two ID3v1 tags — one at the beginning, one at the end of the file, or when files hat two ID3v2.x tags, (illegally) concatenated one after the other.
Usually, such things stem from using a bad (non-compliant) tag writer.
Using CTRL+R twice usually (but not always) helped.
Florian, I've already thought of all those things. My version is always the latest development build and the options are set to remove all tags. I think it happens only on MP3 files.
Moonbase, it's probably something like that. And yes, usually CTRL+R twice helps but sometimes I have to repeat it even more.