In my case I select and try to open about 10-20 mails at the same time. My folders are usually IMAP. Might be that some internal background processes like mailbox polling or perhaps changing the window focus are influencing this.

As I said the issue happens seemingly intermittently with about 50-50 chance for myself. Cannot figure out the pattern.

Hello!

Have anybody besides me noticed in pmail ver 4.70 (build 546) some oddity: when selecting a bunch of emails in a folder view ("shift + mouse click" or "ctrl + click") and after such selection by further pressing "open" or "move"- sometimes all the mails are opened in separate window (as expected) but sometimes this opening operation is performed only for couple of first selected mails intead of all selected. 

I haven't figured out what influences this intermittent behavior but it seems to me as some kind of bug.

I can not duplicate the problem.  I ran repeated tests selecting 3 messages at random and then clicking 'Open".  All opened in individual windows as expected.  The windows are stacked sequentially (top message is the bottom window) which should be helpful to identify whether specific messages cause the failure.