This is occurring on the 4.11 branch as of 1/8/2016.
Editing (or adding a new variable) to a Blueprint Struct with the Default Values view expanded causes a crash of either something related to a Slate text widget not getting a proper size (common UMG crash it seems) or causes one of these much more concerning crashes:
Fatal error: [File:D:\depot\Engine\Source\Runtime\Core\Private\GenericPlatform\GenericPlatformMemory.cpp] [Line: 139]
Ran out of memory allocating 18446744072564227002 bytes with alignment 0
I also have a crash video showing this exact problem. You’ll first see that I do a little trick to hide the Default Values category, which lets me change the 2nd struct variable from a Skeletal Mesh type to a Skeletal Mesh Asset ID. When the Default Values category is expanded, doing the same action on the 3rd struct variable causes a crash. I can reproduce this crash on the 2nd variable, as well as any variable, and by adding a new variable, by simply having the Default Values category expanded.
I can’t attach the crash video as it exceeds the 5MB limit. The crash video can instead be downloaded from my dropbox here: Dropbox - StructCrashVideo.avi - Simplify your life