This was originally reported in Debian: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=449533 but it still happens in recent version (2.28.1 here).

IMAP folders that are created/modified/deleted on a other client (or a webmail) are not updated immediately in Evolution.

Here are two particular test cases:
1. On an IMAP account without "Show only subscribed folders", 
 - when a folder is created on a other client/webmail, it will then be visible in Evo in "Folder->Subscriptions" but will not appear in the tree panel until Evo is restarted
 - when a folder is deleted on a other client/webmail, it will disappear from the tree only after having gone to Folder->Subscriptions (or after a restart I guess)

2. On a Gmail IMAP account (with "Show only subscribed folders"), if a new label is created on the webmail:
 - it will sometimes appear as subscribed on the Folder->Subscriptions menu but sometimes not
 - then, if the folder is marked as subscribed it will appear in the tree after having refreshed the server in Folder->Subscriptions (or after a restart)
 - deletion is the same as in case 1

The expected result would be that Evo reflects remote changes on IMAP folders immediately.