After complaining about the missing documentation of supported id3v2.4 frames in a recent post, I accidentally discovered that foobar2000 maps the RELEASE DATE metatag to the id3v2.4 TDRL frame!
What a joy!
But along that, I also found that the tag writer will not write any values longer than 4 characters.
The id3v2.4 structure documents clearly defines that timestamp format up to YYYY-MM-DDTHH:mm:ss accuracy can be specified.
Instead, if a value such as 1990-09-24 is entered, it is written in a TXXX frame rather than in the correct frame (TDEN, TDOR, TDRC, TDRL or TDTG)
This looks like a bug, since this behavior is appropriate for id3v2.3, not id3v2.4.