why compiler try use my sqrt not std.math?

[KnightMare]

compiler should select right sqrt by arg types. it shouldnt 
prefer my sqrt( ulong ) over std.math.sqrt( real ) when I pass to 
sqrt real with explicit cast

it has from std.math
float sqrt( float )
double sqrt( double )
real sqrt( real )
I added
ulong sqrt( ulong )
and try invoke sqrt( real(SomeVal))
we have real arg, so call std.math.sqrt( real ). no doubt!
WHY compiler tries be too much smart and looks stupid and buggy?

in case no misunderstanding what ceil should be called I missed 
this BUG (compiler call MY sqrt(ulong)) before some tests or 
debugging session