The problem is in two parts, when you are using a tool (Move / Rotate / Scale) in the SceneComposer :
I Don’t know if it’s a feature or a bug, but with or not shift you can use the tool in the scene composer. (for example you can move a spatial in scene while moving the view - with shift)
This one is a bug. When you do the following action (see below) with any tools the action you will not be able to undo it.
actions :
hold shift
hold left mouse button
hover a tool (quads)
do some modification
release left mouse button
release shift
try undo the modification
The bug is easier to see when your modification is different from the last one (for example do scale or rotate after a move)
Ps : I already find an solution on the last version of the SDK, and test it (with build ect …). I order to contribute with more scenecomposer features and want to start with this “fix” to learn how to make a good issue and pull request on git.