It could be a wonky sensor but it could also be a software issue .One thing to try would be to go to Brother's website and see if there is an upgrade for the software. I can't count how many times I have seen goofy issues with software, especially when going from one OS to another, XP to Vista, Vista to 7 ..etc. etc. I have dealt with Brother printers over the years and the one thing I discovered early on is that some of their software is uhhhhh a little different. At any rate if all else fails, purge the software, reload and take a look on their site to see if there are updates/upgrades for that unit, citing, of course your OS, good luck!