Lets say it is normal practice for Yobit. It blocks wallets when there is a pump of certain coins or they have own interests in trade, if you deal with Yobit get ready for such surprises.
This ain't happening to them but I've experience in some exchange too, the timing is perfect where there are pumps.
But if its yobit then you better choose another exchange, don't get used to the complains and better search a well performing exchange.
I also encountered this problem sometime ago when I tried deposit some coins in Yobit. I kept waiting for days for them to fix the issue but I finally had to give up because I realized nothing was being done about it.
Too many complains about their deposits that never stops, check their ANN threads to see more complains.