WLMail – how to retain the position of a folder after moving it?

I'm having a problem retaining the position of a moved folder - in this case Storage folders (as seen in the screenshot below).

In other words, when I move it to the place I need it to be (by using the 'Move up' option on the right-click menu), it returns to its original bottom position whenever I restart WLMail - which is very frustrating. How do I stop this from happening please?

Btw, I've also tried moving the mail accounts (using the 'Move down' option) below the Storage folders, but the same thing happens.