External Tool hangs before running

[aib]

Hi, I have an external tool, a batch file that compiles an actionscript source code.
Whenever I run the tool, it hangs, with the Tool Output empty for a few seconds before executing the .bat file. What can I do?

Tool settings:
Command: (path to bat file)
Parameters: $File
Init. Folder: $FileDir

[x] Capture output

Regex is the default: ^\([^(]+\)(\([0-9]+\)):
Regs: 1 / 2 / (empty)

I don't have this problem on another computer with the same settings, and I did not have it last week, since when no configuration was altered.

My batch file is a simple one:

@rem *** Batch file to compile an actionscript class using the Flex SDK ***

@set SRCFILE=%1
@set COMMON_CLASSES="(directory)"
@set SDKPATH="C:\SDK\flex-2.0.1"
@for /F %%F in (%SRCFILE%) do @set DSTFILE=%%~nF.swf

@echo Compiling "%SRCFILE%"...
%SDKPATH%\bin\mxmlc.exe %SRCFILE% -compiler.source-path=%COMMON_CLASSES%

[aib]

I've just noticed that this only happens on a particular file (actionscript source code; text with ~1k lines)

The tool runs fine on other source files; starts executing immediately...

Note that it's not the compiler waiting; it always takes a few seconds to run, AFTER the echo line...