I found another minor UI bug/inconsistency in Slic3r v1.2.3: While the repositioning of a multi-part object works correctly (in that the part is correctly moved as a whole after releasing the mouse), only the selected part of the mutli-part object gets dragged across the screen.
A quick screencast below:
System: Ubuntu 14.04 64bit
Slic3r: v1.2.3 64bit
I love those animated screenshots :P
Bugfix: when dragging an object, only one part was moving. #2467