Maybe I missed it (in this weird, weird thread) but what brand of strings was Flea using at the time? That seems like it would matter. Someone should know.
Now, to hijack things, the only strings I've broken - outside of ones I kept removing/restringing/swapping - were two strings from the same set of Dean Markleys. I think it was when they first came out with those "cryo" strings or whatever horse hockey that was. It was a five string set, but I don't remember which ones broke. But one broke between the nut and tuner, the other near the middle. And I'm a gentle player.
I asked my bass teacher about it, because he was currently in a death metal band and played HARD. Almost slap tone through fingerstyle. And he said in his 30+ years of playing, the only bass strings he'd ever broken were DM's.
I've done unspeakable things to DR's and never broken a one. And yet, I broke two DM's in one set. Has anyone else had a similar experience with this brand?