We disabled our Steem dollar to Bitcoin conversion pathway a few days ago because our wallet was occasionally reporting a Steem input twice (which would cause us to send out bitcoin twice). This wasn't happening very often, but it was potentially a serious concern, so we disabled Steem inputs until we had a workaround. I don't think this was a problem for other exchanges, as I believe they are relying on scanning blocks for transactions, whereas we poll the transaction history and it seems likely the bug is in the transaction history code.
I'm happy to say we found a workaround: we're using what's called a "delayed node" that waits for about 30 seconds to allow the account history to "settle down" before we send an output, and we believe this should prevent the problem for now. As a longer term solution, we plan to investigate what's causing the false reports, but this gets us going for now. We had to make several fixes for the delayed node code to get it working on steem (this is technology developed originally with bitshares, but looks like it had never been tested with steem) and we'll submit our fixes to the steem repo.
If we don't detect any further problems, we expect to enable Steem to Bitcoin conversions soon as well.