When the "umbrella affect" occurs it is usually because of user error...
No, it's ***ALWAYS*** user error.
To put it simply, look at the math.... on a very basic level, cams are simply variable width stoppers, with a couple very goofy limitations WRT placement... they tend to move at the slightest provocation, can walk their way out of a placement, have no holding power when tipped out due to limited bearing area on the lobes.... which can lead to the cam "umbrella-ing" as the tips of the lobes yield...
I simply don't understand why people think they're the end all be all of climbing gear, as cams have just as many limitations as anything else, if not more.