[Qgis-developer] wrong distance after feature buffer selection in meters, please help

[Julia Philipps]

Hello,

I am trying to develop a plugin for QGIS with C++, but my skills are  
that of a beginner.
So far I have managed to let the user select a point and make a buffer  
around this point, depending what value (in meters) the user chose, to  
select other points within this radius. Now I realised, the distance  
is false. With the measure tool I measured the distance between the  
points, but there are some points missing that should lie in this  
radius.
My guess is that I messed up the Crs? I am confused. Could someone help me?
The projects map units are meters. On the fly projection is enabled.  
The layer on which the plugin operates has the WGS 48 crs.

Sincerely,

Julia P.