It sounds like another defect of Synaptics TouchPad V7.5. I know of no way of certainly provoking the effect, and therefore checking would take much time. I suppose this can be fixed by unchecking some other setting of Synaptics TouchPad V7.5. This then has to be removed by pressing Esc. You just save this in a file, double-click it to run the script and the problem is gone :) I highly recommend you try AutoHotKey for that or any other automation tasks in windows. Much less frequently, moving the cursor on the screen produces the unwished effect of opening the - I don't remember what it's called - visualizing not only the charms but the whole panel on the right edge of 'Search Share Start Devices Settings'. It turned out it took three lines in the script to disable CTRL+scroll zoom in the whole of windows: MaxHotkeysPerInterval 500 WheelDown:: return WheelUp:: return. The related less annoying problem remains.
Surely this is a defect of Synaptics TouchPad V7.5? The action of moving the cursor along the screen is not the same as pinch-zooming.
I no longer have to repeatedly use Ctrl-0 to return to normal size. I have waited a few days to be sure and can now say with certainty that unchecking the pinch zoom in Control Panel /Hardware and Sound /Synaptics TouchPad V7.5 /Settings solves the problem of the changing of the screen font size.
