4 files changed, 20 insertions, 2 deletions
diff --git a/indra/llui/llfloater.cpp b/indra/llui/llfloater.cpp
index 39a6855273..22d6f6ca52 100644
--- a/indra/llui/llfloater.cpp
+++ b/indra/llui/llfloater.cpp
@@ -451,6 +451,14 @@ void LLFloater::enableResizeCtrls(bool enable)
 	}
 }
 
+void LLFloater::destroy()
+{
+	// LLFloaterReg should be synchronized with "dead" floater to avoid returning dead instance before
+	// it was deleted via LLMortician::updateClass(). See EXT-8458.
+	LLFloaterReg::removeInstance(mInstanceName, mKey);
+	die();
+}
+
 // virtual
 LLFloater::~LLFloater()
 {
diff --git a/indra/llui/llfloater.h b/indra/llui/llfloater.h
index 3ea035777c..42f422f91c 100644
--- a/indra/llui/llfloater.h
+++ b/indra/llui/llfloater.h
@@ -308,7 +308,7 @@ protected:
 	BOOL			getAutoFocus() const { return mAutoFocus; }
 	LLDragHandle*	getDragHandle() const { return mDragHandle; }
 
-	void			destroy() { die(); } // Don't call this directly.  You probably want to call closeFloater()
+	void			destroy(); // Don't call this directly.  You probably want to call closeFloater()
 
 	virtual	void	onClickCloseBtn();
 
diff --git a/indra/newview/llmoveview.cpp b/indra/newview/llmoveview.cpp
index 6ae4a5e5e4..fc41137686 100644
--- a/indra/newview/llmoveview.cpp
+++ b/indra/newview/llmoveview.cpp
@@ -83,6 +83,16 @@ LLFloaterMove::LLFloaterMove(const LLSD& key)
 {
 }
 
+LLFloaterMove::~LLFloaterMove()
+{
+	// Ensure LLPanelStandStopFlying panel is not among floater's children. See EXT-8458.
+	setVisible(FALSE);
+
+	// Otherwise it can be destroyed and static pointer in LLPanelStandStopFlying::getInstance() will become invalid.
+	// Such situation was possible when LLFloaterReg returns "dead" instance of floater.
+	// Should not happen after LLFloater::destroy was modified to remove "dead" instances from LLFloaterReg.
+}
+
 // virtual
 BOOL LLFloaterMove::postBuild()
 {
diff --git a/indra/newview/llmoveview.h b/indra/newview/llmoveview.h
index d463861188..43b0342744 100644
--- a/indra/newview/llmoveview.h
+++ b/indra/newview/llmoveview.h
@@ -51,7 +51,7 @@ class LLFloaterMove
 
 private:
 	LLFloaterMove(const LLSD& key);
-	~LLFloaterMove() {}
+	~LLFloaterMove();
 public:
 
 	/*virtual*/	BOOL	postBuild();