To Reproduce:
1 - Create a new Project and create a Widget Blueprint.
2 - Open the Widget Blueprint and drag a Image widget to the canvas.
3 - By default the image have a Size X of 100, click to edit it, manually select the number “1” and type “2”, press Enter to confirm and then press CTRL+Z to undo, the engine shall crash.
More Info:
If I click to edit the value and just type a new value replacing the old number completely, it won’t crash.
But if I manually replace only one number as the example above or add a number, for instance setting it to 1000, it crash when doing a undo.
Happens with any widget.
Tested on 4.14, no crash there.