What happened?

to easily demonstrate this use this macro while targeting yourself:
#showtooltip
/dismount
/use [mod:alt]Great Purple Elekk; Cenarion War Hippogryph
/use Great Purple Elekk

target (in this case you) castbar instantly fails and vanishes
player castbar functions normally

i first noticed it happening in battlegrounds. where target castbar claims opponent failed/stopped casting, when i can obviously see they are chain nuking me or healing. ofcourse there i couldn't communicate with them to see what their macro was doing.

Is there any errors?

No response

Game Version

The Burning Crusade Classic

Game Language

English

Does the issue still occur when all other addons are temporarily disabled?

Yes, issue still occurs.

Any additional info?

No response

Will look into it, but seems to only happen for the player on the target frame, and not other units.

Edit: Should be fixed now.