If focus is taken away from the viewport window in blueprints (LMB in the details pane, for instance), pressing W, E, or R to change the transform widget will not work until focus is returned.
1. Open Editor (any project)
2. Select and open any blueprint with a static mesh component
3. In blueprint viewport, select the static mesh component.
4. Select viewport to provide focus on viewport
5. Press W,E, or R to see transform widget change
6. LMB in Details Pane
7. Press W, E, or R to change transform widget again
Transform widget doesn't change if focus is not directly on viewport.
Transform widget changes as details pane cannot receive direct focus.
There's no existing public thread on this issue, so head over toAnswerHub just mention UE-19595 in the post.