Windows 7 64-bit, GTX 770 OC
Blender 2.78.5 5c96312
While Tweaking Strip Actions (Tab), if the actual keyframes of the action are different from the NLA's relative location, Alt+RMB doesn't select them in the Graph Editor. They can be selected correctly in the Dopesheet.
For example, if the Action's first keyframe is set at frame 0 while the NLA track starts at frame 45, the key can't be selected this way in the Graph Editor.
edit: also Timeslide (Shift+T) doesn't work correctly in Dope Sheet during Tweak mode. It will only work if the cursor starts in the exact frame range (not the NLA's offset range)
edit2: Pose Breakdowner also doesn't work correctly in Tweak Mode. Again, it doesn't account for the offset of the active NLA Strip. Also changed title since there's probably something else.
edit3: moving keyframes in the Graph Editor starts by jumping back to the actual keyframe locations