Cascading Select loses second option when changing issue in Opera

After updating (from 3.2 to 3.4.3!), I have noticed that the second option is sometimes lost when changing an issue.

This doesn't happen with all issues. When I edit or resolve the issue, the custom field for our account/subaccount shows the main account, but the sub account says 'Please select...' It is clearly set when looking at the issue. If I submit my changes, the secondary option is lost.

As people are making updates to the issues, we are losing this data rapidly!