There is -- in my perception -- a problem with the interaction between font style and font size changes.
The order of calling for example  \it\small matters because \small\it leads to a different result.
I would however reason that size and style changes should be in orthogonal spaces, that is: the one should have no effect on the other.
Cause of this behaviour seems the \tf call included in small. See the accompanying example.

I can try to program around this, but I would prefer not to. Is there a possibility that this behaviour will be changed to \it\small and \small\it giving the same result?

dr. Hans van der Meer