Unable to delete swc files in Flash Builder after building using an ANT script - flash-builder

Question

I'm trying to incorporate an ant build script to be used in the FlashBuilder IDE, but I am running into an issue when trying to delete a swc file that is created when running the 'clean' target.
I get the error that "Problem Occurred"
'Deleting files...' has encountered a problem. Problems encountered while deleting resources.
Problems encountered while deleting resources.
Could not delete 'C:\project_src\trunk\flash\labs\bin\commonUtilities.swc'.
Problems encountered while deleting files.
Could not delete: C:\project_src\trunk\flash\labs\bin\commonUtilities.swc.
This error occurs even when I try to delete by right clicking from the Package Explorer in Flash Builder. When I try to delete it from Windows Explorer I get an error stating that FlashBuilder.exe is using the file. This makes me suspect that somehow Flash Builder has locked this file. In order for the clean to work I need to close FlashBuilder and then reopen it.
One interesting note, is that once I reopen Flash Builder and if I do a clean/build repeatly just ONLY the swc project it works without fail, BUT once I try to do a full build with the main project, linking does the 'lock' happen.
This problem does not occur if I am using the default "Flex" in the Builders under the Properties for the project. It only occurs when I import and use my own build file.
I'm extremely new to ant and using the flex compiler. I'm using the to compile my swc file. Does the some how cause FlashBuilder to hold on to the swc file produced?
Buildfile: C:\project_src\trunk\flash\master-build.xml
clean-labs:
[delete] Deleting C:\project_src\trunk\flash\labs\bin\commonUtilities.swc
BUILD FAILED
C:\project_src\trunk\flash\master-build.xml:37: Unable to delete file C:\project_src\trunk\flash\labs\bin\commonUtilities.swc
Total time: 614 milliseconds
I'm using the following:
[echo] ANT_HOME: C:/apache-ant-1.8.4
[echo] flexTasks jar location: C:/apache-ant-1.8.4/lib/flexTasks.jar
[echo] FLEX_HOME: C:/Program Files (x86)/Adobe/Adobe Flash Builder 4.5/sdks/4.5.0
[echo] BRANCH_BASE: C:/justice_src/trunk/
[echo] DEBUG: false
Here's the target for clean-labs:
<target name="clean-labs">
<delete verbose="true" failOnError="true">
<fileset dir="${BRANCH_BASE}/flash/labs/bin/" includes="labs.swc" />
</delete>
</target>
The build target for the swc for the compc part is as follows:
<compc output="${BRANCH_BASE}/flash/labs/bin/commonUtilities.swc"
debug="${DEBUG}"
locale="en_US"
incremental="true" >
The build target for the main project is using and includes
<compiler.library-path dir="${BRANCH_BASE}/flash/labs/bin/" append="true">
<include name="commonUtilities.swc" />
</compiler.library-path>
Does anyone have any idea what is going on? Any thoughts on solutions and workarounds are greatly appreciated.