GPOs being applied, but they're not
I've got a weird one.
On my XP image, the GPOs (deployed from a Server 2008 R2 server) used to work fine, yet for some apparent reason, they're now failing to apply properly. RSOP and GPResult both say the correct GPOs are being applied, yet their effects (such as shared drive remapping, software deployment or printer sharing) aren't materialising. Sysprepping and deploying to a workstation doesn't change this behaviour. Active Directory home folders are working fine.
On a fresh, clean XP install the GPOs are still working fine, so I'm wondering if there's a corrupt file or something on my image or if I'm missing something obvious. There's nothing appearing in Event Viewer which arouses suspicion - no errors or warnings at all.
Has anyone come across such an issue before?