possibly serious bug....need someone from HP...

[parisse]

You are confused: there is a difference between a function f and an expression g. A function has arguments unlike an expression. If f is a function, you can compute f(2) or f(x) and get an expression, while g(2) or g(x) does not mean anything.
Regarding solve, it solves polynomial-like equations, i.e. equations that can be rewritten like a polynomial equation, your equation can not be rewritten like that. For more general equations, there is no method for exact solving, you must switch to approx solving (fsolve). You can solve an expression=another expression with respect to a variable, but solving a function=another function does not mean anything : with respect to what would you solve?. I will add a check to avoid the calc reboot in this situation.