Custom form for Calendar needs frequent cache clearing

Hi, We have a custom form which our Outlook 03/07 users can enter details of
forthcoming change requests. There are 3 tabs on this form normally but we
have recently noticed that one of the tabs is intermittently missing. It is
easily resolved by manually going to Tools > Options > Other > Advanced
options > Custom Forms and then selecting "Clear Cache". The missing tab is
then available to the user.

Can anyone shed any light on why this cache clearing is required and how we
can go about preventing it from being a necessity?

Thanks in advance.