In game 1057217 just after move 122, I set up a lengthy conditional move sequence following the attack I believed my opponent was making. After considering the game a bit longer, I decided that I might have better opportunities than allowing that sequence to play out, so I went back into conditional moves and cleared them. I then double-checked the conditional moves to make sure that they were clear, and they were. (This is important to this story.)
My guess as to my opponent’s line of attack was correct, and moves 123-128 played out as the conditional moves that I had canceled.
This is similar to, but different from, Bug: cancelling conditional moves doesn't work.
In this case following circumstances (including my opponent failing to press a particular attack) caused the conditional sequence to be no worse than what I might otherwise have played, but … it could have lost me a game. I hope there are logs such that this can be analyzed.