I encountered this strange problem in my 4.5 project. I created a custom structure with a linear color parameter and then this happened:
I can set the values back to the normal range, but a few seconds later, even before I can hit OK, the editor either crashes and my mouse is moving really slow until I dismiss the “UE4Editor.exe has stopped working”-message OR I get the regular submit crash report window.
I tried deleting the structure and create a new one, but I get the same problem again.
I found out it’s only happening, when your custom structure is named “Color”. As soon as you try to to edit anything inside it, it crashes. This didn’t happen until 4.5.
What is probably happening is the word “Color” is predefined in code somewhere else, so naming your structure this is causing your issue to occur. I suggest just adding a letter and an underscore to make it more definitive and unique. For example “S_Color”. Let me know if this changes your outcome.