The IMAP implementation had quite some issues when Outlook 2013 got released initially. With update KB2837618 came a drastic amount of fixes and changes to improve the IMAP experience. If your version of Outlook is 15.0.4551.1004 or higher, you have the fixes applied.
However, a downside of this update is that it requires you to configure a “Root folder path” if your IMAP requires it. If you don’t set it, you could end up with folders not synching or not being visible at all.
You can set your root folder path via: File-> Account Settings-> Account Settings…-> double click on your IMAP account-> button More Settings…-> tab Advanced.