Crash undoing variable change in Animation Blueprint.

Crash occurs when the user changes a variable in the animation blueprint, and then undo's the change.

Note that this occurs with any variable being used, but the callstack will be some what different depending on what the variable is affecting.

Crash with variable affecting skeletal controls:

[Link Removed]

Crash with variable affecting blendspace:

[Link Removed]

1. Open QAGame in editor.
2. Open the animation blueprint AnimBP_Blend in Persona.
3. Change the value to the Crouch to Stand Blend variable.
4. Undo.

RESULT:

Crash.

VCRUNTIME140!<Unknown>
UE4Editor_Engine!FExposedValueHandler::Execute() animnodebase.cpp:517
UE4Editor_AnimGraphRuntime!FAnimNode_SkeletalControlBase::Update() animnode_skeletalcontrolbase.cpp:39
UE4Editor_Engine!FPoseLinkBase::Update() animnodebase.cpp:188
UE4Editor_AnimGraphRuntime!FAnimNode_SkeletalControlBase::Update() animnode_skeletalcontrolbase.cpp:34
UE4Editor_Engine!FPoseLinkBase::Update() animnodebase.cpp:188
UE4Editor_AnimGraphRuntime!FAnimNode_SkeletalControlBase::Update() animnode_skeletalcontrolbase.cpp:34
UE4Editor_Engine!FPoseLinkBase::Update() animnodebase.cpp:188
UE4Editor_Engine!FPoseLinkBase::Update() animnodebase.cpp:188
UE4Editor_Engine!FAnimInstanceProxy::UpdateAnimationNode() animinstanceproxy.cpp:40
UE4Editor_Engine!FAnimInstanceProxy::UpdateAnimation() animinstanceproxy.cpp:751
UE4Editor_Engine!USkeletalMeshComponent::PerformAnimationEvaluation() skeletalmeshcomponent.cpp:1159
UE4Editor_Engine!USkeletalMeshComponent::RefreshBoneTransforms() skeletalmeshcomponent.cpp:1333
UE4Editor_UnrealEd!UDebugSkelMeshComponent::RefreshBoneTransforms() debugskelmeshcomponent.cpp:418
UE4Editor_Engine!USkinnedMeshComponent::TickComponent() skinnedmeshcomponent.cpp:542
UE4Editor_Engine!USkeletalMeshComponent::TickComponent() skeletalmeshcomponent.cpp:752
UE4Editor_UnrealEd!UDebugSkelMeshComponent::TickComponent() debugskelmeshcomponent.cpp:735
UE4Editor_Engine!FActorComponentTickFunction::ExecuteTickHelper<<lambda_aa79ebd94b2c9e6b2d520765e2e11e5e> >() actor.h:2937
UE4Editor_Engine!FActorComponentTickFunction::ExecuteTick() actorcomponent.cpp:702
UE4Editor_Engine!FTickFunctionTask::DoTask() ticktaskmanager.cpp:251
UE4Editor_Engine!TGraphTask<FTickFunctionTask>::ExecuteTask() taskgraphinterfaces.h:868
UE4Editor_Core!FNamedTaskThread::ProcessTasksNamedThread() taskgraph.cpp:932
UE4Editor_Core!FNamedTaskThread::ProcessTasksUntilQuit() taskgraph.cpp:679
UE4Editor_Core!FTaskGraphImplementation::WaitUntilTasksComplete() taskgraph.cpp:1776
UE4Editor_Engine!FTickTaskSequencer::ReleaseTickGroup() ticktaskmanager.cpp:520
UE4Editor_Engine!FTickTaskManager::RunTickGroup() ticktaskmanager.cpp:1426
UE4Editor_Engine!UWorld::RunTickGroup() leveltick.cpp:705
UE4Editor_Engine!UWorld::Tick() leveltick.cpp:1236
UE4Editor_Persona!FAnimationViewportClient::Tick() animationeditorviewportclient.cpp:697
UE4Editor_UnrealEd!UEditorEngine::Tick() editorengine.cpp:1472
UE4Editor_UnrealEd!UUnrealEdEngine::Tick() unrealedengine.cpp:371
UE4Editor!FEngineLoop::Tick() launchengineloop.cpp:2834
UE4Editor!GuardedMain() launch.cpp:156
UE4Editor!GuardedMainWrapper() launchwindows.cpp:126
UE4Editor!WinMain() launchwindows.cpp:202
UE4Editor!__scrt_common_main_seh() exe_common.inl:264
kernel32!<Unknown>
ntdll!<Unknown>