My Grancabrio 2010 has exactly the same problem, the sequence in which it happened was, first the steering wheel buttons started blinking whenever the car was cold started, then after 5-7 mins worked fine;
A week or so after completely stopped working, and with it the “roof operation not available” showed;
The fault message is intermittent, yet the roof works fine (i just need to wait to when the message disappears),
The key in door solution works;
The dealership in Doha, Qatar, could also not pinpoint the problem,
One noteworthy mention;
I think this happened after i wiped the sticky buttons on my stereo (display) unit to clean them; (more specific - the numbers pad and volume turner under the screen).
I DID NOT clean the buttons on the steering wheel though,
By the way, Doha is always hot compared to the other posters here that noticed it was temperature related.
i really hope maserati comes up with a diagnostics method teaching their dealers to pinpoint the exact problem;
i am 90pct sure its electrical/static/wiring related, nothing to do with sensors, but a simple defect in the tiniest button / electric short / is surely behind this annoying issue;
keep this blog alive until we have a solid / cost logical solution