Why this happens
This is natural behaviour for this phone - it is part of the power saving modes etc. The reason the menu buttons don't light up in the day - is that you can already see them!! Its like your house lights at home.... you don't have them on during the day.... try a test... use the phone on your desk in the light & then use it hidden under a coat etc... The lights will only come on when it is dark... its not a fault its actually quite clever if you think about it...