For a while I thought that the buttons of my unit became somewhat sticky and stopped changing their setting but then I discovered a solution: I press them mostly from the front towards the back, not from top to bottom. This way they never stick and are able to change the settings every time. I hope this will work for you too.I can no longer change the filter on my Qutest. I had set to orange for a while, then I decided to go back to white, which requires cycling through the other filters, and it's stuck on the red one. I unplugged it for a while and tried again, but no joy. Any suggestions?
However it is a weakness of design as I have read others complaining for the same situation. I hope @Rob Watts / Chord will take this into account for any future designs - or hopefully drop this aesthetically controversial button scheme.