When the message gets moved back to inbox either by d&d or filter, it is detected with new UID with \Seen and \Recent set. This makes it look like a new message to the Inbox filter and it looks like Buik so the filter moves it back to Bulk. I'm not clear how many filters you have normally running and how email gets into Bulk in the first place; only by server-side filtering/delivery?
Bug 1582981 Comment 14 Edit History
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When the message gets moved back to inbox either by d&d or filter, it is detected with new UID with \Seen and \Recent set. This makes it look like a new message to the Inbox filter and it looks like Buik so the filter moves it back to Bulk. I'm not clear how many filters you have normally running and how email gets into Bulk in the first place; only by server-side filtering/delivery? Edit: Maybe this is a server problem. A message seen and read in folder B maybe shouldn't appear \Recent (new) when moved to folder A. Not sure there is mention of this in RFC 3501.