I am using version 4.5.1 and I have tested with only the PF theme extension loaded. The problem is only aesthetic, does not affect functionality.
All "windows" look bad in the top area near the new bar. It is particularly evident for images/maps, other records also have some imperfections but it's more subtle.
Here are some pics
https://imgur.com/a/uZ9hSxi
https://imgur.com/a/k4aQlew