I haven't been playing my 650 D for a while (back on bass for the last year and a half), but I broke A LOT of D strings on that guitar right before I "became" a bass player again...
Used Ernie Ball's for a LONG time before I got the Dakota...so I'm not really sure if it was bad strings or what. My guess is that it was - some years ago the guitarist I play with had a rash of broken D's when he got a 12 pack of D'Addario.
Still, if you were bending, you might have gone a little too far. Especially if they were a different tension and/or guage than you're used to. If they were your normal strings, then it's probably a bad string.
Above e-mail is inactive. try ed_ardzinski@**** where **** is Hotmail.com or Yahoo.com. I tend to see things inthe hotmail box quicker...