Defender TD5 Clutch Switch

Here's a strange one, i noticed today that if I revved my engine with the clutch in it holds the revs a bit before letting them drop. Thinking it was probably the clutch switch I unplugged it, but it still does it and only with the clutch in.

If the clutch switch isn't plugged in then why would it be holding the revs?

It also reads backwards - says ON with the clutch up, and OFF with the clutch down

2000 Defender TD5