Very strange 1 tick pulse bug

I had 2 monostable circuits going into 2 double pistons (see picture) I expected that both monostable circuits would do the same.

Instead the left button works as I expected but the right button does something different at the double etenders.

How to reproduce:
1. build the setup
2. press the left button
3. notice that both piston extenders leave the block.
4. press the right button
5. notice that the right piston leaves the block but the left leaves the piston.