Incremental compile causes a "Variable xx is not defined" error with embedded resource

[Problem]
=========
The customer got "Variable xx is not defined" error when they compiled the project.

More details are as below:

1. the customer found that the error will not show up without following code.

[Embed(source="/images/stopSign-icon.gif")]
public static var lc_stopSignIcon:Class;

2. the customer found that if they set incremental="false" in build.xml, the error will not show up.

STEPS TO REPRODUCE:
===================
1. change following parameter to work path in build.xml.
base.dir
FLEX_HOME
ANT_HOME

2. run build_swf.bat.

3. modify src/Test.mxml. (add a new line)

4. run build_swf.bat again.

5. run flex/Test.swf, following error will show up.

ReferenceError: Error #1065: Variable CommonIcon_lc_stopSignIcon is not defined.

at flash.display::MovieClip/nextFrame()
at mx.managers::SystemManager/deferredNextFrame()[E:\dev\4.y\frameworks\projects\framework\src\mx\managers\SystemManager.as:278]
at mx.managers::SystemManager/preloader_preloaderDocFrameReadyHandler()[E:\dev\4.y\frameworks\projects\framework\src\mx\managers\SystemManager.as:2627]
at flash.events::EventDispatcher/dispatchEventFunction()
at flash.events::EventDispatcher/dispatchEvent()
at mx.preloaders::Preloader/timerHandler()[E:\dev\4.y\frameworks\projects\framework\src\mx\preloaders\Preloader.as:515]
at flash.utils::Timer/_timerDispatch()
at flash.utils::Timer/tick()

RESULT:
=======
compile error shows up

EXPECTED:
=========
no compile error

[System environment]
====================
Flex 4.6.0
apache-ant-1.8.0
use Ant to compile