Confirmed with Inkscape 0.46+devel r22026 on OS X 10.5.8, happens with single objects (not grouped) as well.
settings: scale stroke width off, use geometric bounding box, snapping off, no visible grid
1) draw rectangle, set precise size while in rectangle tool
2) change to select tool, select rectangle and change width or height values (choose even numbers for easier demonstration)
3) numbers are approximated, only repeated entry of the same new value gets it to stick (3-5 times)
Confirmed with Inkscape 0.46+devel r22026 on OS X 10.5.8, happens with single objects (not grouped) as well.
settings: scale stroke width off, use geometric bounding box, snapping off, no visible grid
1) draw rectangle, set precise size while in rectangle tool
2) change to select tool, select rectangle and change width or height values (choose even numbers for easier demonstration)
3) numbers are approximated, only repeated entry of the same new value gets it to stick (3-5 times)