If they show up again, then Bitcoin Core is rebroadcasting them (perhaps to try to get them mined?).
That worked. if Bircoin-qt is not relaying why did they show up in the first place?
Bitcoin-Qt was relaying them (I had some of that dust, too). It but it wasn't re-relaying them, so clearing the mempool made them go away.
It's possible, if you restart Core, that its memory pool will clear allowing them to be re-relayed again if someone rebroadcasts, but I think the newer versions of Core should reject them as non-standard and not relay them.
I think that is it. they got into Armory's memory pool before I had upgraded Bitcoin-QT and it didn't go away until I cleared it. thx