Have you tried the different search parameters?
In the ‘Find’ box, under ‘Criteria’ you’ve selected ‘Keywords’ and then typed in ‘Act 06’ but have you left the parameter as ‘contains’? Try change contains to ‘equals’. Also see if changing search result to match ‘if all criteria are met’.
I’m on CS5, and still getting my head fully around Bridge’s keyword capabilities and searching for them but when I’ve thought Bridge has failed in searches, it has usually been me not setting the parameters correctly. You can also do a lot by searching for multiple keywords and using the negative parameters like does not equal or does not contain. Play around with them and see if they make a difference.