That's capacitive touch for you
For some reason the digitizer needs better earthing (through a firm grip on the device) to work on Sailfish than on Harmattan. I think it is due to some calibration that would be needed on the device to make it more sensitive, and that's missing on MER so the digitizer works on default sensitivity.
Some people experience this behaviour on Harmattan, also, so it is not that uncommon.
I'm not an expert here (no warranty for this method) but you can take a try to flash a closed mode kernel, remove the warranty warning, and flash open mode & ubiboot back. In worst case you'll end up reflashing, what you were to do.