Duplicate range tombstones

I don't have a way to reproduce this just yet, but I have the sstables to prove it and can provide those offline. What I can reproduce, however, is the magnification of this problem via compaction. Here's what I know so far:

• under some condition, we flush the exact same RT more than once in the same sstable. Same timestamps, everything.
• Once this happens in multiple sstables, compacting them causes the duplication to grow. The more this occurs, the worse the problem gets.

This continues until gc_grace has passed, then they are all evicted normally. I'd at least like to take a look at the compaction amplification for now, that way if the condition does occur, at least compaction can help it, rather than exacerbate it.