My car often/mostly doesn't start first time when the engine is already warm.

Cold starts are fine.

It has been suggested to me than some sensor may be causing the engine to be fed fuel as though it is cold, even when it is warm.

Could this be true?

My fuel economy has not been brilliant lately, but not disastrous. 10.7 litres/100km last tank, 98 octane fuel, mixed driving.

Just come across this post, and I've got a 360GLT.... These engines seem very touchy with hot starts - almost always, I have to wait 10secs or so and try again.
I remember my pair of 740s (B200E engine) were the same.

I did wonder whether it was overfuelling (probably account for the woeful economy ) but my local volvo specialist confirmed my suspicions that "They all do that Sir"

I remember, a few years back - I worked in Sweden for the military, and had the use of a Swedish Army 240 staff car for a while - that seemed to start the same.

+1 they all do it. Something to do with a leaky capacitor.

Leaking injectors and bad one-way valve at the fuel pump can also cause this. My problems with this issue went away when I had my injectors refurbished and also swapped the fuel pump to better flowing one. (Which had a working one-way valve also)

A bit rough hot start is normal with these engines but if it doesn't start at all or you have to start it multiple times or for a long perioid of time then it is not normal.

Also there is a cold start circuit which in faulty condition might be overfueling the engine but broken time temperature switch or cold start injector aren't the most common problems I think.