[4.7.3] Engine crashes on compile of one blueprint only if child of that blueprint is also opened in another tab

This is a strange bug. If I open one of my blueprints (“Building”) and compile it, everything works. But if I have another blueprint opened in another tab and this other blueprint is a child of “Building” then the Engine crashes ~10 seconds after I hit compile of Building, before it’s crashing it’s just freezed.

I tried it now 4 times, it crashes every single time if the child blueprint is opened.

Here you have a Callstack and the log, I compiled “Building” two times, then I opened one child blueprint and tried to compile Building again.



I am using the latest 4.7 branch from github.

Hi John,

I wasn’t able to reproduce this in the latest 4.7.3 (from today). Your log actually shows a successful compile of Building before the crash, so I’m guessing the crash is happening when the child tries to update.

Does this only happen with that one Parent BP, or does it occur with others? Does it occur with any children, or just one? If you create a new Actor BP and create a child, does the same crash occur?

4.7.3 from today is actually the same as 4.7 branch from yesterday since the last commit was 2 days ago.

It actually only happens with one child (“CivilHouse”), not with all childs.
I have noticed this bug only with “Building” and “CivilHouse”, not with any other Parent/Child combinations. So if I create a new Actor BP and a child the crash of course does not occur.

Hi John,

Thanks for those details. Since it’s only happening with that Parent/Child combo, can you zip and attach those assets here so the developers can take a look? Thanks!

Actually, I’ve asked for the project in your other post, so if you can get me that I’ll use it to investigate both issues.

Sure, here they are: link text

Hi John,

I was able to reproduce this in your project with the Building and CivilBuilding Blueprints. I’ve created a bug report for the issue (UE-12136), and I’ll let you know as soon as I see any update on it.

Hi John,

Just wanted to give you an update that this has been fixed in our main internal build, and the fix should be included in the 4.8 release.

Thanks! You can’t imagine how often I accidentally had both of these blueprints opened and tried to compile one of them in the last weeks/months without thinking about this bug. Really nice to hear that it’s fixed in 4.8.

I understand that must have been frustrating. Please let us know if this behavior pops up again after 4.8 is released. I think we’re doing a Preview shortly, so you’ll be able to test it there.