Some Bundles Showing up late or disappearing

We are running Zen 11.1.0 on Windows XP sp3 and Windows 7. We have seen instances where a bundle will appear minutes after a user logs on and all other bundles are already present. Sometimes they will disappear too. These are easy bundles like shortcuts to apps installed on workstations. GW Instant Messenger is one example that is consistently late to arrive.

Any ideas?