Redstone left side preference doesn't always work

Despite the "left side bias" introduced in this snapshot redstone will randomly ignore it.

Reproduction Steps

• Build this setup
  
• Hold right click to keep pressing the button

Observed results

• Right side piston sometimes activates

Expected Results

• Only the left side piston would ever activate

Extra info

• For some reason the left side bias has a higher chance of failing with a button as the power source. If you replace it with a lever for example and flick it rapidly the right side piston will activate very rarely