The rain sensor operates from an infra-red beam fired onto the screen from the little box behind your interior mirror. The angle that this reflects back at determines the amount of moisture on the screen and therefore the frequency and speed of the wipes.
If there were dust or other crap on the thing which sends the beam, could this be the root cause?
If they bashed (even ever-so-slightly) that thing, could that be it the cause?
If they put on a screen that indeed wasn't made for cars with rainsensing wipers, could this be the cause?
These are pure speculation you must understand but logical ones born out of knowing how it works and having spent hours daydreaming, wondering why this happened to me on my Focus Ghia.
I didn't ask any questions or get that bothered because it was a company car going back in a couple of days.
The long and short of it is that you paid Autoglass to repair your vehicle back to the standard of how it was before and they haven't so they need to sort it....
Might not help but hope you get it sorted, let us know how you get on as this is going to become a more widespread problem with the incresed standardisation of this feature.
JJ
You gotta tie yourself to the mast my friend, and the storm will end.