Actually the tipping still works, there's still some SBD on the account to handle the tips. The problem occurs if someone tries to withdraw all deposit since many users did it before. But @tipU is still earning new SBD each day so with time things should balance out.

By the way, this SBD pump might be exchanges inside job. I'm writing about this here:
https://steemit.com/steem/@tipu/dont-send-sbd-steem-to-poloniex-they-are-probably-doing-inside-trading-now