Attempt to remove child: isc_HTMLFlow_0_eventMask

I am seeing an exception when closing a tab that contains an HTMLFlow which I do not recall seeing before. I have been trying to track down the source of the exception but haven't had any luck yet. Any thoughts at to what could have introduced this exception? It doesn't appear to have an impact on functionality.

1. SmartClient Version: v9.1p_2014-04-29/Pro Deployment (built 2014-04-29)

2. FF ESR 24.5.0

3.
11:09:13.935:MDN1:INFO:clears:isc_WorkflowHTMLFlow _4:clear() (2 children)
Canvas.clear(_1=>undef)
Canvas.removeChild(_1=>[VLayout ID:isc_WorkflowHTMLFlow_4], _2=>undef)
Layout.removeChild(_1=>[VLayout ID:isc_WorkflowHTMLFlow_4], _2=>undef)
TabSet.removeTabs(_1=>Array[1], _2=>undef)
TabSet.removeTab(_1=>[SimpleTabButton ID:isc_OpswiseTab_17], _2=>undef)
TabSet.closeClick(_1=>[SimpleTabButton ID:isc_OpswiseTab_17])
TabSet.$52a(_1=>[SimpleTabButton ID:isc_OpswiseTab_17])
TabBar.tabIconClick(_1=>[SimpleTabButton ID:isc_OpswiseTab_17])
[a]SimpleTabButton.iconMouseDown([IMGElement]{name:isc_IXicon}, null, Obj)
Canvas.$wd(_1=>"icon", _2=>"mouseDown", _3=>[IMGElement]{name:isc_IXicon}, _4=>null, _5=>Obj)
Canvas.firePartEvent(_1=>Obj, _2=>"mouseDown")
StatefulCanvas.handleMouseDown(_1=>Obj, _2=>null)
[c]EventHandler.bubbleEvent(_1=>[SimpleTabButton ID:isc_OpswiseTab_17], _2=>"mouseDown", _3=>null, _4=>false)
[c]EventHandler._$observed_doHandleMouseDown(_1=>[object MouseEvent], _2=>undef)
doHandleMouseDownObservation([object MouseEvent], undef)
[c]EventHandler.handleMouseDown(_1=>[object MouseEvent], _2=>undef)
[c]EventHandler.dispatch(_1=>[c]EventHandler.handleMouseDown(), _2=>[object MouseEvent])
anonymous(event=>[object MouseEvent])

11:09:13.939:MDN1:INFO:destroys:isc_HTMLFlow_0_eve ntMask:destroy()
Canvas.$75s(_1=>true, _2=>undef)
Canvas.destroy(_1=>undef, _2=>undef, _3=>undef, _4=>undef, _5=>undef)
[c]EventHandler.unregisterMaskableItem(_1=>[HTMLFlow ID:isc_HTMLFlow_0])
Canvas.clear(_1=>true)
** recursed on Canvas.clear

11:09:13.942:MDN1:WARN:VLayout:isc_WorkflowHTMLFlo w_4:Attempt to remove child: [Canvas ID:isc_HTMLFlow_0_eventMask] from Canvas that is not its parent
11:09:13.951:MDN1:DEBUG:PaneContainer:isc_OpswiseT abSet_0_paneContainer:delaying adjustOverflow: childClear
11:09:13.970:MDN1:INFO:destroys:isc_WorkflowHTMLFl ow_4:destroy() (1 children)
Canvas.$75s(_1=>true, _2=>undef)
Canvas.destroy(_1=>undef, _2=>undef, _3=>undef, _4=>undef, _5=>undef)
TabSet.removeTabs(_1=>Array[1], _2=>undef)
TabSet.removeTab(_1=>[SimpleTabButton ID:isc_OpswiseTab_17], _2=>undef)
TabSet.closeClick(_1=>[SimpleTabButton ID:isc_OpswiseTab_17])
TabSet.$52a(_1=>[SimpleTabButton ID:isc_OpswiseTab_17])
TabBar.tabIconClick(_1=>[SimpleTabButton ID:isc_OpswiseTab_17])
[a]SimpleTabButton.iconMouseDown([IMGElement]{name:isc_IXicon}, null, Obj)
Canvas.$wd(_1=>"icon", _2=>"mouseDown", _3=>[IMGElement]{name:isc_IXicon}, _4=>null, _5=>Obj)
Canvas.firePartEvent(_1=>Obj, _2=>"mouseDown")
StatefulCanvas.handleMouseDown(_1=>Obj, _2=>null)
[c]EventHandler.bubbleEvent(_1=>[SimpleTabButton ID:isc_OpswiseTab_17], _2=>"mouseDown", _3=>null, _4=>false)
[c]EventHandler._$observed_doHandleMouseDown(_1=>[object MouseEvent], _2=>undef)
doHandleMouseDownObservation([object MouseEvent], undef)
[c]EventHandler.handleMouseDown(_1=>[object MouseEvent], _2=>undef)
[c]EventHandler.dispatch(_1=>[c]EventHandler.handleMouseDown(), _2=>[object MouseEvent])
anonymous(event=>[object MouseEvent])

5.
11:09:13.943 [ERROR] [opswise] 11:09:13.942:MDN1:WARN:VLayout:isc_WorkflowHTMLFlo w_4:Attempt to remove child: [Canvas ID:isc_HTMLFlow_0_eventMask] from Canvas that is not its parent
com.smartgwt.client.core.JsObject$SGWT_WARN: 11:09:13.942:MDN1:WARN:VLayout:isc_WorkflowHTMLFlo w_4:Attempt to remove child: [Canvas ID:isc_HTMLFlow_0_eventMask] from Canvas that is not its parent
at sun.reflect.NativeConstructorAccessorImpl.newInsta nce0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInsta nce(NativeConstructorAccessorImpl.java:39)
at sun.reflect.DelegatingConstructorAccessorImpl.newI nstance(DelegatingConstructorAccessorImpl.java:27)
at java.lang.reflect.Constructor.newInstance(Construc tor.java:513)
at com.google.gwt.dev.shell.MethodAdaptor.invoke(Meth odAdaptor.java:105)
at com.google.gwt.dev.shell.MethodDispatch.invoke(Met hodDispatch.java:71)
at com.google.gwt.dev.shell.OophmSessionHandler.invok e(OophmSessionHandler.java:172)
at com.google.gwt.dev.shell.BrowserChannelServer.reac tToMessages(BrowserChannelServer.java:293)
at com.google.gwt.dev.shell.BrowserChannelServer.proc essConnection(BrowserChannelServer.java:547)
at com.google.gwt.dev.shell.BrowserChannelServer.run( BrowserChannelServer.java:364)
at java.lang.Thread.run(Thread.java:695)