Dripping Shower Head

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I have a trigger controlled shower head fitted with an isolation valve. It is used to wash in addition to a bidet.The trigger operates perfectly when it is used but water drips from its head when it is hung on its bracket. The water trapped in the flexi-pipe drips down from the head with the isolation valve fully shut. This leakage causes considerable puddle and dampness on the floor. I do not understand why does it leak with the isolation valve closed? Can this leakage be stopped? Any professional advice would be appreciated.

 

[Alanka]

Can it be the slow thermal expansion of the water 'stored' in the flexi-hose, when the shower is switched off? The expanded water would drip out of the shower head, and continue to do so until all expansion had stopped. This could only happen, of course, if the water starts off at below room temperature and gradually warms up - which I admit doesn't seem likely!

Does the dripping slow down (and stop) as time passes?

How do you know the isolation valve and the trigger shut off 100% - they could be letting a tiny amount of water pass - enough to cause dripping.

Try removing the hose and watching the outlet from the shut isolation valve for a while, to see if any water appears.

This effect sometimes happens with conventional showers for a while - but you don't notice the dripping so much because it falls into the shower tray, rather than on the floor. A theory: the water stored in the hose and in the mixer valve housing when the flow is shut off is gradually expelled via the shower head as the hose and housing cool down and contract in volume (more than the water, presumably)???

 

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Thanks Big Al for detailed response.
The shower in question is fed from a thermostatic mixer valve set at moderate temperature.
The dripping stops eventually but too late to avoid a puddle!
The isolation valve is 100% shut as I have removed the flexi hose and there is no dripping from the valve.
I am not sure about the shower head side i.e. the trigger's efficiency. I thought with isolation valve shut and a good shaking of shower head with trigger on before hanging up should be sufficient to avoid dripping.