Played some more again, lovely game :D
Sometimes the game doesn't make sense. bug/butterfly rule has to be "even" or "higher" based on 4 on 1 being ok, thus 8 on 4 must be ok but isn't.
There was no rule change. I did however click outside the game to write something down and then back in (browser version). This is the 3rd time in ~8 games. Not sure always related to clicking out of the game.
It just happened again. 1 on 2 ok means odd or -1 or less thus 6 on 1 shouldn't be ok. I put 5 on top of that and it was ok.
I guess sometimes npcs don't get flagged for being wrong under specific circumstances.
oooooh, I had assumed that "0" is both lower than 1 and greater than 9 and only when a "0" has been played, any other number is greater than and less than at the same time.
PS: Does this mean that if the rule is +1, I can place anything on a "0" card? I was assuming I have to place "1" on "0" on +1 rules. [edit] ah yes, looking at ai's behavior anything goes in that situation...