Had the same problem with Pegasus and Thunderbird both configured that MercuryI only supports trays (not like directories on filessytsem capable holding directories and files: folders holding mails and subfolders). Created them with Pegasus and all seemed good. closed Pegasus and opened Thunderbird. All seemed good too. Next day opened Pegasus @work and all trays have been at root.

OK ... tried deleting the trays - which resulted in editing HIERARCH.PM by hand .

Created a hierarchie of trays and folders some days later and it seems to be stable. May be your moving of trays resulted in same stability (didn't try that, so don't know if it had worked in my case)?!

May be it is an initial problem on new IMAP-Mailboxes or first time creating a tray with subtrays? Just my suggestions ...

bye   Olaf

Something strange. When creating an sub folder in PM, it's appear as an root folder in IMAP client, and the other way round, when creating an sub folder in IMAP client, it's appear as an root folder in PM. Moving the IMAP folder, in PM, for it's right place as sub folder everything  is in the right place.

I don't know if it is PM or Mercury, both latest versions, but it's new, because all the old sub folders are in the right places.

//stig