Spark Label throw an RTE when truncating text

Steps to reproduce:
1. Create a new Flex Project and run the following code:
<?xml version="1.0" encoding="utf-8"?>
<s:Application xmlns:fx="http://ns.adobe.com/mxml/2009"
xmlns:s="library://ns.adobe.com/flex/spark"
xmlns:mx="library://ns.adobe.com/flex/mx">

<s:Label text="This text is too long to fit in the 100px width on one line, so it may be truncated, which causes the RTE."
width="100" maxDisplayedLines="1"/>

</s:Application>

Actual Results:

Execution throws an RTE (translated from French):
ReferenceError: Error #1069: Property -1 can not be found at _AS3_.vec.Vector.<flash.display::DisplayObject> and there is no default value.
at spark.components::Label/truncateText()[E:\dev\4.0.0\frameworks\projects\spark\src\spark\components\Label.as:1246]
at spark.components::Label/http://www.adobe.com/2006/flex/mx/internal::composeTextLines()[E:\dev\4.0.0\frameworks\projects\spark\src\spark\components\Label.as:485]
at spark.components.supportClasses::TextBase/measure()[E:\dev\4.0.0\frameworks\projects\spark\src\spark\components\supportClasses\TextBase.as:533]
at mx.core::UIComponent/measureSizes()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\core\UIComponent.as:8042]
at mx.core::UIComponent/validateSize()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\core\UIComponent.as:7966]
at mx.managers::LayoutManager/validateSize()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\managers\LayoutManager.as:617]
at mx.managers::LayoutManager/doPhasedInstantiation()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\managers\LayoutManager.as:709]
at mx.managers::LayoutManager/doPhasedInstantiationCallback()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\managers\LayoutManager.as:1072]

Expected Results:

• No RTE
• The text should be truncated

Workaround (if any):
None found