sometimes when you stop with the wipers on they stop (at junctions)when you move off they start again !

thats nothing,,, when l turn my cold water tap on, hot water comes out of the hot water tap

When l studied Rocket Science at Teck l was told there are two washer pumps on a Megan washer bottle, 1 for front screen and 1 for rear.
It could be an evil Goblin has cast a spell on the Megan or an extraneous current is jumping between the wires causing the wrong pump to function, but more likely the pipes are connected up wrong or the wiring connectors have been swapped over.

Sounds to me like you have a crossed supply hose.

Its French what do you expect. My one does the same l think its something the little frogs add on to keep us interested and amused

sometimes the washer bottle has two motors, so it sounds like the wires are back to front.if its only got one motor..then the feed hose is on the wrong outlet most likely

there is only 1 washer pump fitted to your car and supplies water to front and rear washers by the ecm/bcm changing earth control(the washer pump works both ways) This might not directly answer your question however the pump is your main cause, change the washer pump and your problem should be cured!
Faulty washer pump!

The wipers are supposed to be intelligent and stop and start to match your driving. Big feature in the adverts a few years ago. The washer pumps were probably cross connected by a dyslexic frog