OST allows you to view and interact with some of your mailbox content if Outlook is offline.  

Yep, I know the OST is a local store

but, in Outlook uncached mode/setup there should be no OST, as its online/live only .
Thats the whole point of uncached .

Ive had cases of Outlook bugs , were things worked better in uncached mode/setup. Yet the OST was still created .
?-)

What's your local policy look like for Microsoft Outlook.  There's a setting there to allow/deny creating an OST.  In Cached Mode settings there's a few options on what to do with the OST, e.g. no OST or simple OST for Calendar, etc.