In VectorGeometry.pas line 3364 must be
d:=d-c2PI;
instead of
d:=-d-c2PI;
This bug was introduced in revision 1.38 of original file Geometry.pas (see [1]), apparently in order to fix VectorAngleLerp() but is no longer used there.
[1] http://glscene.cvs.sourceforge.net/viewvc/glscene/Source/Base/Geometry.pas?view=diff&r1=1.37&r2=1.38
This is a rather complex procedure and I don't understand what it is supposed to do. If you post a small demo of this bug, I may be able to confirm it and commit your bugfix.