Ubuntu 20.04 5.4.0-48-generic
GeForce GTX 1080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 440.100

Blender 2.91 master build from 8335c26119bf5ba78b2afa4e2f65bb3d04b42abe

Short description of error
Measure tool multi 3dview and quad view inconsistencies

Exact steps for others to reproduce the error
Open default scene. Enable Measure tool in toolbar and add a measurement.
Enable quad view with ctl+alt+q.
Go to top view and adjust measurement. Do not do anything else.
Do the same with front and side view, you now have 4 different measurements visible.
You can zoom, move and rotate views and you still have 4 measures, but if you select an other object it will change to the last adjusted measurement.
Same if you split 3dview.