In reply to BruceWee:
> Anyone had a similar experience and found a solution apart from concentrating on relaxing the foot as much as possible?
Sounds like it's one of possibly two things. Either you've a pair of footbeds in your ski boots that are raising the arch of your foot too much, which seems unlikely seeing as it's only when you do them up. Or, and the more likely option, your ski boots don't fit the shape of your feet. Not being an expert boot fitter anything more than the above across the internet is just speculation.
What you do need to do is get yourself to a top class boot fitter get your feet remeasured and either get your boots blown/modified to suit, get a new set of liners, and possibly footbeds, that suit your feet or possibly the most drastic action, though the one most likely to fix it properly, get a new pair of boots that suit your feet. At least if you go for the final option you will have the likelyhood of being able to sell on your existing boots.
Where are you based? maybe possible to get a recommendation of a good boot fitter in your region who will help sort you out.