Squrrelmail and IMP - controlling 'Sent' and 'sent-mail' folders

An unexpected but welcome change occured with IMP for one account that I’d like to get a handle on server-wide for any account that uses IMAP. After using the account for a few months, IMP had at some point started using ‘Sent’ instead of its regular ‘sent-mail’ folder and did so without any config changes, which is fine.

I am guessing the change happened because Squirrelmail’s “Base sent messages” folder was defined as ‘Sent’ which IMP now understands. So when I create a test account and set Squirrelmail this way, IMP continues to use ‘sent-mail’. I need for IMP to behave just like Squirrelmail as much as possible, especially with sent messages.

So my question is: What caused IMP to change its mind and start using ‘Sent’ for sent messages instead of its regular ‘sent-mail’ folder? I’d like it this way always. Should I just reconfigure once and for all and which files need to be changed to control IMAP folders and namespace for IMP?

Suggestions appreciated.