[Lazarus] Code navigation sometimes doesn't work

[Lubos Pintes]

Hi,
I opened lcl.lpk package. Located some unit and opened it. I am on 
Windows so am interested in Windows stuff.
So for example I opened win32\interfaces.pp and tried to find 
implementation for CreateWidgetSet. I was placed somewhere in some uses 
section of some unit. Why?
Also for DebugLn, or PEventHandler. But switching between interface and 
implementation of class TWin32WidgetSet worked fine.
Why is that?