I see this bug many times in old relises of SC, and it was one of things why I don't upgrade from free edition. A few day ago I come back to idea make an upgrade (you make a awesome work!) and was very surprised that bug still exist.
You can easily found this here for example
(great game btw)
Sometimes controlled character (object) don't move in this or that direction from keybord. (You can press button many times but character "stuck") But if you press opposite direction move button, he start going.
Step by step: controlled character don't want to move right. Press button "move left" (opposite direction) once, now controlled character can move in needed (right) direction again.
Usually, it happened close to screen (game) borders or close to another textures/object with "solid" properties.
It will be very good, if someone can fix it. This is very annoying.