I've not encountered that problem with mine.
I couldn't recall to what extent I'd moved the thing around just holding onto the drill (thus far, I've used it exclusively with Centrotec drills)... so I've just tried it out and I cannot pull the drill from the drive shank without releasing the chuck sleeve, however hard I pull or jerk it, even holding the guide down with the other hand.
Has, perhaps, your Centrotec chuck become a little worn and looser? They work on, essentially, the the same principle that's used on racing car steering wheels and I've had one of those become sloppy over time (but replaced before it became a danger!).
What could well be a problem (when, for example. climbing down a ladder and just holding the drill) is that the carriage might slide up and knock the protecting caps off of the rods and let the rest of the guide drop. I've not yet used it in a situation where that would be a risk, but I do have a couple of extra collar-stops to fix above the carriage to stop that.
(In the interests of balance, I've been very pleased with mine!)
:-)