Game freeze with 360 Controller (Web Version)

[Shambler2]

Situation:
Launching the game and using a 360 controller, using the left stick to select a level and pressing A to get in.

Attempting to move either left or right with the left stick the game freezes. Also seems to occur with the right stick

Does not occur if you use the D-Pad instead.

Jumping occurs fine, appears to just be the input from the Left stick.