Excel: how to permanently apply conditional formatting to the whole spreadsheet?

I have the following annoying problem with Excel 2010. I use Conditional formatting to apply bold formatting to each line of the spreadsheet that meets a condition expressed by a formula. In the "applies to", I write =$A$2:$Q$149, which is the current extent of my spreadsheet. But I want this range to grow with my spreadsheet, i.e., I want the formatting to permanently apply to the whole spreadsheet. Regularly, my "applies to" field is transformed into a complex range, that selects most lines of spreadsheet, but not all, like =$A$2:$Q$138;$A$140:$Q$147. Have you ever encountered such a problem? Is there a solution?