So it's a bug even considering

7.5.5 Math italic mess

of the reference luatex.pdf ?

--

luigi

Section 7.5.5 is very vague, its example of  \mathitalicsmode=0 or 1 show no difference (more exactly: I am unable to see any difference).

When we keep the example 1.$f!$, 2. $f$!, 3. $f\/$! and we say, that italic correction inserted is correct in all three cases (as XeTeX does it), then we can see:

\mathitalicmode=0:  1. OK, 2 bad, 3. bad

\mathitalicmode=1:  1. OK, 2 bad, 3. OK

\mathitalicmode=2:  1. bad, 2 OK, 3. OK

It is magic.

Petr