This has been a reoccuring problem not only in the 7.1 OS. My GF's Bold 9900 had the same problem with the factory BNIB OS 7.0. Not sure what it is, but when i upgraded her phone to the latest OS from Desktop Manager it seemed to have fixed the problem. Not sure what i can tell you, but try reinstalling the OS.
The first OS that came with my 9900 was horrible for that especially in the browser. The other versions I've tried from crackberry didn't have this issue, but it came back in this one.