[SOLVED] How do I use functions defined with Func in the solve function?

How do I use functions defined with Func in the solve function?

Say I have this function defined using Func:

Define f(x)=Func
              Return x²
            EndFunc

I can use this function in most cases perfectly fine:

f(2)            © 4
f(3)+f(4)       © 24
cos(f(sqrt(π))) © -1
expand(f(x+1))  © x²+2⋅x+1

However, when I try to use this function in solve or cSolve (possibly some other functions as well), it doesn't work as expected:

© I expected 'x=-2 or x=2'
solve(f(x)=4,x)   © f(x)=4
© I expected 'x=-2⋅i or x=2⋅i'
cSolve(f(x)=-4,x) © f(x)=-4

It doesn't seem to expand/evaluate the function call and leaves it as f(x).

On the other hand, if I don't use Func, it works perfectly fine:

Define g(x)=x²   © Done
solve(g(x)=4,x)  © x=-2 or x=2
cSolve(g(x)=4,x) © x=-2⋅i or x=2⋅i

nSolve works for both f and g as intended, so this makes me think it's something to do with symbolic computations.

Is there any documentation about this difference? I've looked over the relevant sections of the reference guide and the guidebook, but have found nothing.
Is there a way of defining functions using Func (so I can use local variables and things like that) that still work with functions like solve and cSolve?

I'm using a TI-Nspire CX CAS Handheld (the older one, not the CX II).

Solution

I contacted customer support and they responded with

There is not a way to use the function defined the way you did using "func" and "return" with the solve command.