...unless the warranty covers accidents caused by wheeling around in an office chair. 

Or maybe I should check if my traffic insurance covers it!
After all, the chair does have wheels.

Anyway, thanks for the info.

That's right. The "shaft" is a really flimsy looking plastic thing with snap on hooks (sorry, don't a better english term for it).
Does not look solid at all, no wonder they broke off so easily.
The ends of the shafts are literally in many pieces, some still lodged inside the remaining hole.

My fault, of course, but the these are very weak parts. Be careful!