The change detection caching mechanism doesn't seem to work for files that have a space in the first few characters of the name. For example when trying to copy a file using the Copy task that is named "abc d.txt", change detection will throw an exception with a root cause of:
Caused by: java.io.FileNotFoundException: C:\Documents and Settings\sappling\.gradle\caches\0.9-20091106171421-0500\fileHashes\ab\abc \abc d.txt_2c3f1971582743c90f7642656cbc2c0a.bin (The system cannot find the path specified)

I think the "abc " directory is problematic.