Stannah Stairlift 260 doesn't stop at bottom charging point?

My partner's father's Stair lift works perfectly when going to up position. i.e. copper plunger hits slow down flag. Stannah lift slows down and stops as it should with the plunger on the copper recharge pad.
Going down, the plunger hits the slow down flag and then stops just afterwards. This means it is not charging and beeps continuously unless switched off. This would be OK, buts some times due to his age he leaves it on and the batteries lose their charge which means he can't get the chair to take him upstairs again.
One thing of note is that the chair stops every so often for a short time at the charge point in the middle when travelling upstairs. Its like the chair is out of sequence control wise moving downwards.