They started to have problems with BitShares already 8 days ago. I even made a post about it.

https://steemit.com/poloniex/@scorer/poloniex-problems-with-bitshares

Yes, they have disabled BitShares already in the past for many times. I counted at least 3 times and none of them was some kind of error that was discussed in github repository. Even once it was posted there but no info from Poloniex side.