Jroz,
this could be something simple like an intermittent connection on the ribbon cable to the button panel. Heat from the optical block could be enough to break the connection, however...
don't dismantle your projector if it is still under warranty,
get it repaired FOC
bSures have a three year warranty. If you have your original receipt then you'll know how far along the warranty period it is. If you don't have the receipt then you can also tell the age of the projector from the serial number.
You check it like this:
e.g. serial number MV05
042269013666
04 is the year of manufacture
22 is the week of manufacture - about the end of May in this example.
Add 3 months to the date of manufacture to get a rough start date for the warranty period.
Assuming the problem is a manufacturing fault then for the first 12 months of the bSure warranty your projector will be collected, repaired and returned to you FOC.
In the 2nd & 3rd year of the warranty you pay for the carriage to the repair centre. Your projector is repaired and returned to you FOC.
Register a warranty claim by calling the help line - 0800 783 2310
Good luck
p.s. the projector will mount upside down but as you rightly say it uses a special bracket that hooks into the rear feet and a point just forward of the front foot. The pj can also be hung upsidedown in a cradle.