Overlay not working with mesa_no_error set to true

[sheepdestroyer]

• Steam client version (build number or date): Last beta as of 15/11/2019 :
  

• Distribution : Fedora release 31
  Kernel Version: 5.3.9-300.fc31.x86_64
  Driver Version: 3.0 Mesa 19.2.2

• Opted into Steam client beta?: [Yes]

• Have you checked for system updates?: [Yes] : All up2date as of 15/11/2019

HW : i7-3520M : ivybridge with intel GPU HD4000

Please describe your issue in as much detail as possible:

Steam Overlay does not work with performance optimisation option "mesa_no_error" set to true in ~/.drirc ; I just get an empty gray rectangle in upper right corner of my screen. Overlay works fine without this option.

I can consistently make the problem appear and disappear by turning "mesa_no_error" on and off.
It has been the case since at least Fedora 29.

I think I remember reading that this perf optimisation was contributed by Valve