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When using a dry install of 1.6 off of icculus's site, gtkradiant 1.6.20121007, and I use the mouse to right-click and drag any XYZ window (in XYZ/Cam quad layout, 2 button mouse controls) the mouse seems to go a little wonky.
1.4, 1.5 doesn't do this. It's only in the XYZ, camera operates fine.
It's not any particular mouse driver, tried it/reproduced on a completely dry install of windows 7 (I had a spare computer laying around to duplicate). It just seems when I right-click and drag, the selected screen speeds out of control.
Also, right before sending, I tested on an older dual P3 Xeon/Quadro Dell (just an old cad station) and it also does it.
Possibly related to issue #37.