Well, I've just noticed that after editing ID3v2.4 tags in iTunes the tags are ruined - nor foobar2000, nor Mp3tag can read them anymore (Mp3tag displays !BAD before the ID3v2 in my %_tag% column of the File View). However iTunes itself doesn't seem to bother - it displays everything in the same way as it did before editing tags.
(BTW I found an option to recover tags by converting them in iTunes to ID3v2.3 format, everything i had is recovered properly except ORIGYEAR (which is missing) and cover (which is fu***d up))
This does NOT match with ID3v2.3 tags. They work just fine and can be edited in both applications.
Should I move back to older tag format? How come iTunes doen't support ID3v2.4 properly?