Boot closure

[Tourer]

When the weather is hot (like it is today) I experience the following problem when opening the hood.  Pressing the Open button achieves the desired effect namely that the boot lid opens, the roof opens and sinks into the boot and the boot lid closes.  But there is no "ding" and the red strip light across the top of the close button stays lit.  Recycling the roof - i.e. closing it and opening it again sometimes clears the problem - sometimes it doesn't.  The boot lid looks like it's closed properly - just no satisfying "ding".  When the car is parked out of the sun and all cools down it seems to work Ok again.  I'm guessing there must be a switch somewhere that's sticking when it gets hot but where is it?  Or maybe this is not the problem.  Any ideas anyone?

The car is approaching 10 years old so if I need a new switch so be it!