Monitor cloning with Windows 10 and different refresh rates uses wrong refresh rate

Cloning a 144Hz monitor to a 60Hz monitor is behaving strangely on Windows 10.

The display output to the 144Hz monitor is confirmed to be 144Hz, however applications on the 144Hz monitor are only updated at 60Hz, except for the mouse cursor movements and fullscreen directx 9 games.

A second 144Hz display which is not cloned to a 60Hz display behaves normally.

1. 144Hz 1920x1080 DisplayPort
2. 60Hz 1920x1080 HDMI (capture card, clone of display 1)
3. 144Hz 1920x1080 DVI dual-link (extended display)

The issue appears to be related to DWM. Stopping DWM using DisableDWM causes non-fullscreen applications to update at 144Hz properly, but breaks the taskbar and other parts of Windows 10 so is not useful.