Thanks. I am on the Beta (and have been for some years).
About > Version Info reports that I'm on 1.51.4-479. I assume that's the latest Beta?
If it helps, I received three emails in a row, all from senders who have @googlemail.com addresses. The first two were from sender1 (who is in my contacts list), the third was from sender2 (who is NOT in my contacts list). All 3 emails show as coming from sender1 when I have "Replace contact names" checked. They display correctly (i.e. two from sender1 and one from sender2) when I uncheck this settings. I can reproduce the issue by checking/unchecking this setting.