Now it works... But I'm sure it didn't few minutes ago because I've tried it in many ways.

Ok, no it doesn't anymore, and I can't get a file to open in sfplay with a message 'prepend open', even if the filepath it correctly output by the left outlet.

Cycling knows about this bug already - it's related to the "roundness" of the corners. In the meantime, try decreasing the roundness amount, then you'll be able to resize.