When I rename an IMAP account (Configuration->Preferences for current account->Account->Basic->Name of account), the folder settings for the associated mailbox are correctly preserved.  However, folderitemrc then contains two copies of all the folder settings: one set for the mailbox's old name, and one set for the mailbox's new name.  I think the old folder settings (i.e., the ones referencing the previous mailbox name) should have been removed.  At best, keeping the old ones around pollutes the rc file with a bunch of dangling entries; at worst, they might prevent the default folder settings from being applied if the user later creates a new account with the old name.