Bug report: Checkmate while taking back moves

http://en.lichess.org/bnY9nibKslKL

In this position, after taking back a few moves at once, as in spamming the takeback button, the site seemingly couldn't cope with the number of requests (4-6 clicks) and defaulted to a checkmate by the computer.

Strange?

Wow, that is funny.

http://en.lichess.org/fm2WUV0w#116

I manage to produce the same result, but i did it by clicking takeback right before an actual checkmate. Clicking takeback 4-6 times right in succession did not result in a false "checkmate".