Problem drips from new shower

I had an expensive new walk-in shower fitted in my bathroom. It has a shower-pump (due to poor pressure) and a large shower-head (about 7 inches diameter), about 7.5 feet up. The control has a knob for main-shower flow, one for temperature, one for secondary hand-held shower flow.

It's mostly great, the only strange thing is that several minutes after finishing shower (maybe 10 or more) a large quantity of drips is released by the whole shower head, lasting for maybe 30 seconds. This is then repeated once or twice more over the next few minutes, though with diminishing quantities of water. The shower doesn't drip in any other way.

This is not a huge problem, but is a bit annoying as the shower is near the living room, and the water falling down is quite noisy. Also, having maybe wiped the shower screen, it gets splashed again with quite a lot of water (not just a few drips)

Is this normal, or could it be put right. As I said, purchase and fitting of this (by pro-installer) was expensive so i want to be sure it's right. I contacted the technical dept of the large store that supplied it here in UK. They raised the question of whether there might be any debris in the system left from installation or whether maybe shower-valve need a new basket (?) but on the whole but they said it probably wasn't anything to worry about.

I'm guessing that the rainshower head is on the ceiling. The piping must have some horizontal component on the ceiling. Think of a straw when you put your finger over the end then pull it out of the glass of water - the water holds in the straw. Well, when you shut off the valve, the water is sort of like that. I don't think there's much you could do about it.