Remuxed M2TS to MKV gives PGS subtitles without language flag (with Blurip)

[Quasit]

All the subs except the two first English ones are missing the "language flag". In MPCHC/VLC/XBMC it'll just say "Undetermined/Unknown" but still work. Is there anyway to fix this or change some setting so they are properly named?

Here's how it looks in Blurip:


These are the four first subs after the remux is done:

Text #1
ID                               : 3
Format                           : PGS
Muxing mode                      : zlib
Codec ID                         : S_HDMV/PGS
Codec ID/Info                    : The same subtitle format used on BDs/HD-DVDs
Language                         : English

Text #2
ID                               : 4
Format                           : PGS
Muxing mode                      : zlib
Codec ID                         : S_HDMV/PGS
Codec ID/Info                    : The same subtitle format used on BDs/HD-DVDs
Language                         : English

Text #3
ID                               : 5
Format                           : PGS
Muxing mode                      : zlib
Codec ID                         : S_HDMV/PGS
Codec ID/Info                    : The same subtitle format used on BDs/HD-DVDs

Text #4
ID                               : 6
Format                           : PGS
Muxing mode                      : zlib
Codec ID                         : S_HDMV/PGS
Codec ID/Info                    : The same subtitle format used on BDs/HD-DVDs

Text #5
ID                               : 7
Format                           : PGS
Muxing mode                      : zlib
Codec ID                         : S_HDMV/PGS
Codec ID/Info                    : The same subtitle format used on BDs/HD-DVDs

[Quasit]

Well, I did some tests. It seems to only affect foreign PGS subtitles. Also IDX/SUB subtitles get language flag no matter what language.
I guess it's just a Blurip bug.