Certain users have experiences problems when changing bugs that have had other changes made to them since the last time they refreshed their bug data.

Normally Bugzilla would complain and throw up a screen displaying the conflicting changes. In some cases this screen is not shown and the prior changes are overridden with incorrect values. In other cases a screen is shown, the user clicks Back, refreshes the page, resubmits their changes and some values are reset back to previous values anyway.

https://engineering.redhat.com/rt3/Ticket/Display.html?id=30724