King Capture Explanation Wanted

I thought I understood the rules around king capture but I just played a game where both myself and a 2300 thought incorrectly. 

Below is the game on move 13.b it will not allow king capture.  Can someone explain why? Is it somehow because of the yellow queen?

https://www.chess.com/variants/4-player-chess/game/28360034/48/4

I also think that they may have changed the rules since I went back to an old game where there was a possible mate that wouldn't work (at the time) due to a king capture superseding a checkmate.  When I went back to the analysis board today it now says that the checkmate would've won.

Can anyone explain this?

Thanks

If You take yellows king red will take yours.

Therefore taking yellows king is illegal.

I think that in teams taking a king has priority over a check or checkmate.  See below from analysis board where green can legally take red king despite check so I don't think it's the red knight causing the issue.

Simply put, you can't make a move that leaves you in check. If red had played Ne6+ instead of a double check, you'd be able to take the yellow king. 

EDIT: Just saw your previous comment. I think it's a bug

I never saw this before, i tried to take the king and i couldnt because its a double check from red and yellow. If blue is checked by only one side, it allows the king capture. So maybe double check is more important than a king capture? I dont think so, it may be a bug

I think the key is the double check, but I'm pretty sure that this is a bug or an unannounced rule change, since I'm pretty sure I have seen a scenario in the past involving double check (even a checkmate) where the king could still be taken.

I tried on analysis board and here are 2 examples where the only difference is c6 pawn making it single vs double check.  In the first screen, red can take king, second, red cannot take king:

Lol sorry, didnt realize this was teams. I think you should be able to capture yellows king - unless, like rojo said, it has something to do with the double check.

Wait but if both pieces that are double-checking you are the same color, then you cannot capture their king? This should be fixed.

I agree it's a bug.

Imagine if a situation like this happened in a world championship.

Actually now I remember.

The logic is that capturing the Y king does not eliminate the check from Red, hence it's not a legal move. The idea when we legalized king captures was that you could eliminate the threat to your king by eliminating the player and hence his pieces.

This makes sense in FFA. In teams too, I guess it's just a matter of definition, what rules we want. I remember already discussing this in the forum and we decided on the current implementation.

I agree and when in doublecheck from the same player it's def a bug. I've also found what's causing the trouble. I think it is in fact just a bug, and this behavior was only intended for FFA, so I'll fix it.