Odd heating problem

Okay, so my heating/climatronic is a bit bonkers at the moment!

A while ago I started a thread that it was a bit random on the passenger side... http://www.briskoda.net/forums/topic/332899-somewhat-unique-climatronic-issue/ ...but that went away and hasn't resurfaced since. However, it now appears to be playing a whole new game!

Everything sort of is doing what I want in terms of where air should be blowing at the same time, but it just seems to be blowing a lot hotter than it should. A/C is working fine, as is up to full temp. It's just the bit above 'LO' which doesn't feel right, roughly the 16-20 degrees area. If I turn the heat up, it gets hotter as it should, then back down to, say, 16 degrees again and it's a lot cooler, but within a minute or two it seems to gradually creep up to a temp much warmer than it should be on that reading.

Any ideas on this one? I feel it might be linked to the previous problem, but just seems a bit strange since most issues on this forum are with heating systems blowing colder than normal due to blockages or water not getting round the system, but to blow hotter seems a bit weird!