Idling question

I used to have a problem with erratic idling when warm (engine wanted to die at traffic lights, bouncing between 900 and 500 rpm). I solved that problem by replacing the accelerator pedal with a second-hand one in February, as well as replacing a cracked brake servo pipe before that, along with a set of new spark plugs. Being somewhat alert to idling now, I have noticed an odd phenomenon. When cold starting in cold weather the engine immediately idles at 900 rpm, but cold starting in warm, summer weather (i.e., ambient temp of >20C) the engine idles at 1100 rpm, before dropping down to 850 rpm after a minute, when the coolant reaches aroud 45 deg C, as one expects. I would have expected the same behaviour in cold conditions (but to have a high idle for longer).

I suspected a temperamental cooling sensor/connection, but the OBD diagnostics reveal it works in both scenarios.

It isn't a problem (yet) but an explanation would put my mind at ease. Is this normal behaviour? Any advice/comments gratefully received.