Here's the code:
-----
struct Struct(T)
{
    static if (is(typeof(T.nan))) {
        static const is_fptype = true;
    }
    else {
        static const is_fptype = false;
    }

    
    static if(typeof(*this).is_fptype)
    //static if((typeof(*this)).is_fptype) //<- fixes it
    {
        pragma(msg, "T is " ~ T.stringof);
        pragma(msg, typeof(*this).stringof ~ " is fp type");
    }
    else {
        pragma(msg, "T is " ~ T.stringof);
        pragma(msg, typeof(*this).stringof ~ " is NOT fp type");
    }

}

alias Struct!(float) Sf;

alias Struct!(int) Si;

-------

From compiling that I get the output:
"""
T is float
Struct!(float) is fp type
T is int
Struct!(float) is fp type
"""





The output expected is:
"""
T is float
Struct!(float) is fp type
T is int
Struct!(int) is NOT fp type
"""

And that is the output you get if you stick extra parentheses around (typeof(*this)).

This was tested on D1.033.

Possibly related to: 
* http://d.puremagic.com/issues/show_bug.cgi?id=2219
* http://d.puremagic.com/issues/show_bug.cgi?id=2154