Can't understand how stack works

[rumovoice]

I've written following function:

code:
Function KillMyProcess

	; Change current directory to temp

	; to prevent creation of TempWmicBatchFile.bat

	Push $OUTDIR

	StrCpy $OUTDIR $TEMP

	nsexec::ExecToLog "wmic process where name='MyApp.exe' delete"

	Pop $OUTDIR

FunctionEnd

As far as I know $OUTDIR should not change after this function is called, but it equals to 0 instead. I tried to add debug message boxes. Looks like everything goes fine until Pop is called which just sets $OUTDIR value to zero. Why is that?