Admin permission not recognized after room downgrade

[opk12]

• Room A is :matrix.org, version 6. There is a working @rss:envs.net, which is maubot/rss, according to the bot's docs. I am admin and can configure the bot successfully.
• I do /upgraderoom 12. This tombstones A and creates room B, where I have creator / owner privilege.
• In B, I do /upgraderoom 10. This tombstones B and creates room C. I am PL 0 in C, due to an unrelated bug in Synapse.
• I kick the bot out of A and invite it in C.
• Another admin makes me admin in C.
• If the other admin does !rss subscribe ... in C, it works, but if I do it, then it outputs You don't have the permission to manage the subscriptions of this room. instead. We have kicked and reinvited the bot a few times.

[opk12]

Maybe(?) related to a (closed) ticket that the PL stops being recognized after an upgrade to version 12 maubot/maubot#270