Thanks for your problem report! Quoting Gerald Turner <gtur...@unzane.com>:
However newer versions split this information into a separate 'subject' field, which my XMPP client (Pidgin usually) ignores. It's also absent from MUC group messages entirely.
True. I will either remove the subject again or duplicate it in the message, so that it works well enough with (almost) all XMPP clients. Cheers