Hi,
I have a layer containing points with the internal projection as Extended Lambert II (ESRI 102582). The external projection is Spherical Mercator. I use also an OpenStreetMap layer.
As you can see on the picture, there's a shift.
The red triangle is the point shown by thinkgeo. The blue circle is the point in WGS84 (conversion by an external tool). The green star is the point in WGS84 obtained by geocoding using google api. The point represent a drugstore "Pharmacie de la croix bleue".
I've attached a project that reproduce the shift.
Thanks,
P.OM