Bug Report: Deadlock Freeze On Mouse Over Unfocused Editor

when an application like chrome or notepad has its window selected on top, with UE4.15 editor in the background, hovering over UE4 editor buttons often causes a freeze, forcing me to restart the computer.

Repro Steps:

  1. Open UE4.15 editor with a blank project, and select the floor mesh.
  2. Open Chrome or Notepad, windowed on top of editor.
  3. While the other application has focus, hover over details panel buttons like Mobility:Static, Stationary, Movable.


Deadlocked frozen computer, keyboard and mouse frozen, no access to the task manager, youtube music continues to play without a hitch. Hard reboot is the only option left.

Computer specs:

8 Core i7 processor,
16 GB ram,
Windows 7 professional ( 64 bit, Service Pack 1)

this freeze does not seem to occur on 4.13.1

Hello ScottSpadea,

I was not able to reproduce your issue on our end. I tested your issue on several machines with several Operating systems (Windows 7, Windows 10, and Mac) and could not achieve the result you have. I have a couple of questions to help me narrow down the issue you are experiencing

  1. Can you reproduce this crash on a separate machine?
  2. If so, what are the specs on that machine?
  3. What operating system is your computer running?


Do you have any of the software applications in the Webpage here

These softwares do have know compatibility issues and may be causing your issue

no, none of those are installed on this machine.

Hello ScottSpadea,

sorry for the delay in response, I have couple more questions for you:

  1. How long between the deadlock occurring and when you restart the computer?
  2. If you run a project through visual studio debugging could let us know if visual studio gives you an error when the deadlock occurs?
  1. right after rebooting my computer, if i load up 4.15 editor, and do what i described above, it often deadlocks. if i leave the computer running for several days, then load up 4.15 and follow those steps, it also often deadlocks. lately i have been using 4.13.1, and it doesn’t ever deadlock, and no other software on my computer causes deadlocks, even when using zbrush, blender, gimp, ue4.13, and a ton of chrome tabs all at the same time, it causes no problems. so i don’t think its related to the time since the computer was turned on.

  2. i haven’t used visual studio debugging with UE4 before, would i compile the engine in debug mode? do i need UnrealVS Extension?
    would this debugging be capable of throwing an error during a deadlock? because this deadlock doesn’t seem to close the editor or any windows, it just freezes input while allowing sound to continue. would it write errors to a log file or something? i would have to reboot the computer to access any error messages, if they exist… but i thought debugging a deadlock would be limited by the unsolved halting problem.

i haven’t investigated this too deeply, because its extremely frustrating to have to reboot my computer multiple times in a row, trying different things like turning off tool tips, or seeing which rollover buttons cause the freeze more consistently, or opening my computer case and putting a large fan on full blast to make sure things aren’t over heating… but none of these had any effect. if i had a backup computer to work on while i test this, that wouldn’t be as frustrating, but i don’t really want to risk my only machine on testing these freezes.

From my previous post, I think I may have caused some miscommunication about what I meant. What I meant to ask is how long do you wait after the deadlock occurring to reset your computer?

Here are some repro steps to run the debug process through visual studio:

  1. Open the launcher and create a new C++ project (I used the first person shooter Template)
  2. When Visual Studio and the project open, close the project so only Visual Studio is open
  3. In the Solution explorer Right click your project (Screenshot_01)
  4. Find the debug option in the new window and select the option Start new instance (this will now open the editor for the project)
  5. Perform the Deadlock (Have visual studio visible somewhere)
  6. If the project is crashing and causing the deadlock visual studio will generate a callstack. If there is a callstack being generated, the contents of it will greatly help in our investigation of you issue


here is a cell phone video of me causing the deadlock:

the project is not crashing, there are no call stacks, it just freezes the computer.

Thank you for uploading a video. One more piece of information I’d like to have from you is your full DxDiag to help me investigate your issue further.

link text


Your issue may be linked to a series of crashes we are currently investigating, From your DxDiag, you have some similar parts to other experiencing these crashes. You can view this issue here:

4.17 preview 2 seems to have fixed the issue! :slight_smile: :slight_smile: :slight_smile: