MUC subject should not update if there is a <thread/>
Thus saith the xep:
Note: A message with a <subject/> and a <body/> or a <subject/> and a <thread/> is a legitimate message, but it SHALL NOT be interpreted as a subject change.
Thus saith the xep:
Note: A message with a <subject/> and a <body/> or a <subject/> and a <thread/> is a legitimate message, but it SHALL NOT be interpreted as a subject change.