With Pegasus mail v4.91.1746 (the latest released version) some emails appear with a blank subject in the new mail folder view.
When viewing the message the window title is also wrong for example

 Pegasus Mail - [sender email, ??????????????7?????]

(the 7 amongst the ?'s is correct - the number of ?'s may be incorrect). Its also not always a "7"
The message view Subject line is correct - in this example its:

 Subject:    Your parcel has been delivered. How did we do?​

In the raw view for this email the subject is shown as:

Subject: =?UTF8?Q?Your_parcel_has_been_delivered._How_did_we_do=3F=E2=80=8B?=

All the examples of this I quickly checked in my inbox all started

Subject: =?UTF-8?Q?

or

Subject: =?utf-8?Q?

These emails came from a number of different senders.

This did not happen the previous release of pmail (4.81)- and emails downloaded with that version appear correctly in my inbox even though they have a subject starting with the same string (=?utf-8?Q?).

This is from a post to the PM-WIN list:

David Harris wrote about this problem:

===
This is a problem with the format of the index file used in the old v2 folder 
format. If a UTF-8 string is a particular length, it may get truncated in the 
middle of a multibyte character, which renders the entire string unusable. 
When you load and display the message in the reader or preview screen, it 
actually loads and parses the header from the message without using the 
index precis form, so it gets it right.
===

This statement caught me by surprise since this UTF-8 encoding issue has existed for awhile, so I tested it using a message that contained this subject line (copied from the first post):

Subject: =?UTF8?Q?Your_parcel_has_been_delivered._How_did_we_do=3F=E2=80=8B?=

The subject field appeared blank in the new mail folder list in 4.81 and then in 4.91.

This issue is specific to the new mail folder. The content of these subject lines is visible when the message is in a different folder. Surprisingly, the subject content is visible when you move one of these messages back to the New mail folder, but only until the New mail folder is refreshed.

I suppose until we have a fix, a workaround could be to use a new mail filter to move these messages to a folder.

I take this back. Checking for "UTF8" in either the Subject header or with an expression filter does not. We can see it in the raw view but apparently the filter is searching the encoded content. This starts getting beyond my level of understanding.