My solution:

reflash it into a original firmware,then,like you said, you will still having the problem, so return to the nokia care point and complain your warranty,if they say no, try again and be angry if necessary. It worked for me when they said me that the usb port broken problem was because "I pull the charger so hard",I turn angry with them and finally they said me "Ok,we will send your phone to warranty departament,but it is almost sure that they will deny the warranty" Final result? A brand new N900.

hope my story helps you.