System Information
Operating system: 5k iMAC version 10.14.4
Graphics card: and radeon r9 m380

Blender Version
Broken: (example: 2.80,release candate

Short description of error
On multiple monitors one is a 5k iMac retina screen the other is a monitor at 1920 x 1080
after doing a render and the image editor is showing and you hit render again the main menu scale up
but the main blender window should be on the low res monitor and the image editor popup should be on the 5k monitor
the main menu will scale up then after the render is done it goes back to normal size

Exact steps for others to reproduce the error

1. make sure blender is open on the low res screen 1920x1080
2. add a scene that take a little time to render
3. select render image from the main menu drop down
4. when the image editor pops up move it to the iMac 5k monitor
5. hit render again as the render is going on the menu will scale in appearance

see screen shot