Microsoft Excel 2007 highlights multiple cells

I have an ongoing issue…various spreadsheets (none in particular…could be one or two or all of them) will start taking on this behavior for no apparent reason: when you click an individual cell, it highlights that cell plus usually two to the right of it. Reformatting by using the format painter from an unaffected cell (if you can find one at that point that hasn’t been affected) usually corrects it but it’s time-consuming to manually go back and reformat each affected cell. What causes this behavior and how can I stop it? Or is there an easier fix for it? TIA!