[OldG]

I use the area around the bridge to strum freely too, I hit those strings pretty hard when I get 'loose' with it. So, I reckon its some thing else breaking the strings....

some questions to consider here:

Do they break at the bridge end of the guitar?
How old are the strings?
Are you absolutely sure of your tuning being correct and in concert pitch?
Do you use a metal plectrum?
Do you use quality branded strings?

The answer to your problem is probably in the answers to those questions...

HTH
Mick