I think this happens occasioanally, whatever platform (freeview, sky, cable, etc.) you have. It's accepted as just "one of those things".
If it's happening more often than very occasionally then I would say that you do have a problem.
First thing I would suggest is to double-check the position of the 'wands' if you use them. I have noticed, from experience, that if they are mis-aligned by even the smallest amount, channel changes can be very erratic.
If you don't use the wands (ie have set it up to use the 'Front IR Blaster' in Guided Setup) then I might suspect stray IR from another remote control. Either that or possibly bright sun-light; assuming you've had some recently
I'm sure someone else will be along shortly with some other (possibly more accurate) suggestions