Steps To Reproduce:

1. Launch Unity editor and create a new project
2. Make sure the Editor is using METAL ( can't repro with OpenGL )
3. Make sure the Editor window can be completely blocked by the window we are switching to
4. Use CMD + TAB to switch back and forth between the Editor and the other window
5. (Workaround) Once the text distortion happens, keep switching a few more times with CMD + TAB (this should fix the distortion in a few tries)

Expected Result: Unity editor is focused
Observed Result: Texts in UI editor gets distorted

Reproducible On: 2019.3.0a3, 2019.2.0b3
Not Reproducible On: 2019.1.0f1

Environment: Occurs only on Mac

Reproducibility: <1/10

**Not easily reproducible as it doesn't occur every time. But this issue has been observed on a lot on Mac machines.