Just cause you think by the look of something, doesnt mean that it was designed for what you want / think it should do!
I know what the bar looks like as Ive still got one in my shed, but never thought for one minute that even when I started kiting that it should be up to the task of what you tried. More from the fact that there were (as is now) 3 different bar sizes available
Though this does serve as a pointer for others with the same bar to not try the same as they could have similar or worse scenario that you experience. Glad you managed to fix your bar with spares you had
The end on that bar was designed to be able to adjust bar width, that's why it's molded the way it is....very obviously.
It broke because it was sun baked hot, frozen cold, old and used, dried out and brittle or cracked...not because it was misused.
Some bar ends are glued on, some are attached by pop rivet, some use screws, some are glued and riveted, some are glued and screwed and Airush uses a spring loaded push in button (like an Easy Up sun shade).
Eventually many of them go the way this one did, my old Naish just crumbled over time.
Slingshot bar ends seem to hold up better than many others, and they are screwed in at the exact same spot ,before the cover boot goes on.
I have a ten year old Airush bar that is riveted from both sides (on each end) instead of one on the bottom of each end (like the one above), the two rivet on the sides works out well.
If the bar end is not dried out and/or starting to crack along the parting lines, then they are fine.
You can usually see when they are ready to die, if you look at them regularly.
My take away (after my Naish went)...is that I look at my gear closely and fairly often, not had anything funny happen on any part of any of my bars in a long time.