The current implementation of the PROPFILE token does not explicitly close the property file after reading it. This can lead to the property file being held open by the JVM for extended periods, long beyond the duration of the build job. On my Windows 7 build slave, the file appears to be held open indefinitely, and while testing the bug I once even saw two separate file handles open against a single property file. The open file handles prevent the file from being manipulated (deleted, moved, etc.) in Windows.
PropertyFromFileMacro.ReadProperty.call() should explicitly close the input file immediately after calling Properties.load().