Now I'm really clueless. This is the problem (you don't need neither the capx posted above nor any Plugin): in my Project, there is an HTML element. If you touch that HTML element, everything is fine as long as you don't move your finger. At the moment you move your finger just one pixel, "Touch -> Is in touch" condition will stop triggering, and I need this to be true (because it actually is!).
If you want to check this by yourself, you can do it with TextBoxes or Buttons (as they both are HTML elements too): put a big TextBox and a black sprite next to it. If "Touch -> Is in touch" -> "Sprite -> Rotate 1 degree clockwise". You will notice the sprite will stop rotating as soon as you move your finger in the TextBox area. You can simulate touches in Chrome by hitting F12 and then Ctrl + Shift + M, otherwise you won't see the bug.
Is there any walkaround or do I have to report it as a bug?
Thank you for your help!