Slice constraints need additional key pressed to work other than CTRL/Shift?

It seems like you have to press some additional key other than ctrl or shift to make the constraints on the slice tools (drag line) work.
Activate the context cut streamline tool, without any components selected, for example, and click into empty space. Begin dragging the cut line, you can release the hotkey and still drag out the line. But when you press down shift or ctrl, the line just freezes. But if I press any key and then ctrl the constraints work again. This is problematic, when you activate the streamline tool from a radial menu, where you don't have any other key pressed after activation.

Fixed.