XUN does not work like the other cryptonotes. If it did we wouldnt have this issue and there wouldnt be any pre-mine.
sure it does,
in about 6 or 7 hours time; the invalid tx will expire from mempool as it hasn't been committed to a block (expiration occurs after 24 hours) and mining will resume unhindered.
i'd invite devs to include some thorough transaction checking; like satoshi clones do before accepting a tx to mempool.
lets wait and see what actions unfold.
james