To file a bug report, please make a post in the "Bug Report" forum under "Discussion."
There are a couple known issues in the 2016 0.4 port:
Speed - I believe this is due to faster operating systems. The penguin can now move much faster than the window. The speed mod was added to put the original spice back into the game.
Window tracking - Under certain speed modifiers other than 1.0, the window will occasionally abandon chasing the penguin in favor of walking down the edge of the level.