I stumbled upon an issue related to writing ID3v1 tags. When the option "Use text-only genre in ID3v2 tags" is disabled, the genre in ID3v1 (yes, v1!) becomes "Other", no matter which genre was set.

Please look at the ID3v1 tag of the test file I tagged with EasyTAG 2.4.2 ("Use text-only genre in ID3v2 tags" was disabled):

$ tail -c 128 test.mp3 | hexdump -C
00000000  54 41 47 54 68 69 73 20  69 73 20 74 68 65 20 74  |TAGThis is the t|
00000010  69 74 6c 65 20 66 69 65  6c 64 23 23 23 23 23 23  |itle field######|
00000020  23 54 68 69 73 20 69 73  20 74 68 65 20 61 72 74  |#This is the art|
00000030  69 73 74 20 66 69 65 6c  64 23 23 23 23 23 23 54  |ist field######T|
00000040  68 69 73 20 69 73 20 74  68 65 20 61 6c 62 75 6d  |his is the album|
00000050  20 66 69 65 6c 64 23 23  23 23 23 23 23 32 30 31  | field#######201|
00000060  36 54 68 69 73 20 69 73  20 74 68 65 20 63 6f 6d  |6This is the com|
00000070  6d 65 6e 74 20 66 69 65  6c 64 23 23 23 00 63 0c  |ment field###.c.|
00000080

The text fields are padded with # signs on purpose. Notice the last three bytes: 00 63 0c. 00 is the separator byte, 63 is the track number (=99 dec, which is correct), and 0c is the genre ID (=12 dec, which corresponds to "Other"). This is wrong, in this test the track was tagged as "Metal", so the ID should be 09 hex.

When I enable "Use text-only genre in ID3v2 tags" and tag the file again, the last three bytes become 00 63 09. The genre ID is now correct.

As far as I see, the genre in ID3v2 tag is written correctly both as a number, and as text (I viewed the contents of ID3v2 tag using MP3Diags program). In my tests the unexpected behavior only concerns ID3v1 tag.