High back boosters

[Havaianas]

Can anyone help with a practical issue.
We are trying to persevere with the high back boosters (DC age 7)
We have two different ones and have one in each vehicle.
We always carefully make sure the seat belt is correctly and flatly threaded through the shoulder part (ie:underneath the head cushion bit)
The problem we have is that whenever DC reaches forward and then back, the seatbelts stay loose! The belt gets caught in the plastic slot somehow and doesn't retract properly. It's obviously pretty dangerous and quite frankly driving me potty.
I ended up taking the back off the seat last week as I felt it was causing more problems than using just the booster cushion alone but obviously I realise this is not a long term solution and I want to get it resolved, especially with the new guidelines until age 12
Have we just had bad luck in that we've bought two crappy high back boosters? They weren't cheap and they look like they should be effective. Is it a common design fault? Something we are doing wrong with the cars seatbelt?
Any input gratefully received!

[Shetland]

Watching with interest - mine does this too. In our case it's because the slot to feed the belt in is at the bottom of the holder and it drops down there when she leans forward and then can't get out again.
I think I may have to admit defeat and get a different one :(

[BugPlaster]

Does the height need adjusting somehow? I haven't had to adjust mine yet but seem to remember it is possible. Otherwise, I would think your seatbelt is at fault.

[2016ismyyear]

Morning what height is the headrest at?
What seats are they?

[dedicatedfollowerofyellow]

This BBC news article states that backless car seats will be approved for children under age 12 or 135cm once they reach a height of 125cm. On that basic I was planing on keeping DD in her backless booster as she is over 125cm (just) and the seat belt does sit neatly on her shoulder.

We seem to have the opposite problem with DS's booster, the seat belt won't roll in and out so he can't move forward very easily once he is buckled in. It probably doesn't bother him particularly as he was in a 5 point harness seat before that.

[Havaianas]

The headrest is at the full height, ie; fully open if you see what I mean. I've tried adjusting the seatbelt height on wall of the car too but it made no difference. Im wondering if it's because our seatbelts start quite far back, a good few inches behind the seat

[Andbabymakesthree]

There should be a small gap between headrest and child's shoulders. At seven unless he's really tall shouldn't be on max height yet.

Dedicated the seat belt should move with child in accident. If it locks prematurely then more injuries could be caused.