We need more precision:

• are you trying to delete a message from one account's mailbox to the trash of another account or is the trash in the same account?
• if they are the same, do you mean that this does not happen while using only one account?

The problem occurs when I'm trying to move a message from the 2nd account to the trash of that account. When doing drag & drop, the folders of the 2nd account, including the trash, don't get highlighted when I drag a message on them, contrary to my first account.

I've tried all the cases possible and the only one that work is copying/moving from my first (primary) account to a folder in that first account. The others one don't work but the only one I find essential is copying/moving from my 2nd account to my 2nd account

Fixed a bug where the mailbox submenu would simply not show at all.
Fixed the bug with the DnD too among other nice adjustments.