Editing values of a control rig can cause the undo to stop working in Anim Details or Sequencer

It has been observed that the the undo function may stop working after the User changes values of a control rig with the slider in the Sequencer. While using the slider, the value stops chaning after half a second and the "Can't undo while "X" is in progress" is displayed in Edit Menu. 

The issue, so far, happened when:

• setting key values in Sequencer
• changing property values in Anim Details

There is a workaround: user needs to clear the undo history, but the issue may reappear while changing  values again. 

In QAGame:

1. Create a new Blueprint (Character)
2. Set the Skeletal Mesh Asset to SKM_Manny_Simple
3. Drag the new blueprint into the level
4. Create a new level sequence and drag the new blueprint into it. (make sure that the mode is automatically set to Animation Mode)
5. Add a Transform track for the blueprint
6. Drag Location.X in the Details Panel
7. Drag Location.Y in the Sequencer Details

RESULT: The slider stops updating (undo is broken)