I managed to replicate the problem on WinXP SP2. When I repeated the Erase command on the same file, it did erase.
I tried it on several files and the bug seems to occur only with very small files. It may be related to the fact that, in NTFS, small files and directories can be entirely contained within the master file table (MFT) record.
Glad to hear you could replicate similar behaviour.
I tried erasing two pdf files, one at a time. The first file was 80KB and the second was 3.8MB. Neither would be erased on their own, only the archive attribute was cleared, no matter how many times I tried.
If I selected both of them, they were erased first time.