I don't know if the bug was introduced in June '18 v4.73 but I have never noticed it before.
I was receiving Email Notifications for another Forum. Although P-Mail is set to SMTP Time Zone Auto, the notification emails were 1hr off. Looking at the email headers I could see that the email headers were indicating the correct UCT/GMT DST offset.
P-Mail runs 24 x 7 x 365. I had to close P-Mail and retstart it for Time Stamping to be correct.