Graco Trilogic HBB

[moanyhole]

I have been trying to assemble this with DH tonight but when we attach the base to the high back part it doesn't seem secure and wiggles, there is no audible click. It easily comes apart and the connection seems flimsy. Is this right? It doesn't seem like it is but we cannot seem to attach it more securely and google shows up nothing.
HELP!

My mum has a Graco Junior Maxi high backed booster for her car (which I don't actually let my children go in, I swap my Britax Adventure in instead - it's a much better seat and it takes seconds).

Anyway, the back on her Graco one is really flimsy, and if you are not careful lifting it the base falls off as you try to lift/carry it.

I expect it's just like that, because the back is removable. But even the two Britax high backed boosters I have (the Adventure and an isofix one too) have a bit of movement in them, to allow for a bit of adjustment to fit different vehicle seats. They are not rigid, even though the backs are not removable.