> (%i1) declare(f, multiplicative);
> (%i2) declare(f, additive);
> (%i5) f(a*b +c);
> (%o5) f(c) + f(a b)
This is a bug which should be fixed in the next release. In the meantime,
you can do
expand( ... , 0, 0)
which resimplifies the expression without expanding it.