Bees do anchor the combs in a TBH. It's not a big deal, really. If you have room to reach your hand/arm in and cut them free with a knife, do (when working the hive). Otherwise, the perfect hive tool for such attachments is coat-hanger wire end bent at 90 degrees and hammered flat like a blade. Extend it down into the hive, turn the end under the brace comb and slide the wire up and out, cutting the attachments.
They need the brace comb for stability, so don't cut it unless you really need to inspect that comb. They'll reattach it when you're done.