**System Information**
Operating system: Windows-10-10.0.18362-SP0 64 Bits
Graphics card: GeForce GTX 980/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 442.50
**Blender Version**
Broken: version: 2.90 (sub 0), branch: master, commit date: 2020-04-30 20:00, hash: `rB03f4d20bcf7f`
**Short description of error**
Masking is not visible on the level 0 mesh with MultiRes added to the object. Also, the mask is saved on every single subdiv level individually, so if you clear the mask at a lower level the mask will still be there on every level above it (i.e. removing the mask at level 3 will have the mask still present at level 4 and up, etc., etc.).
{F8510031}
**Exact steps for others to reproduce the error**
1) Take a cube and subdivide it.
2) Go down to level 0 and try to mask the mesh, which does not work. Then pick any subdiv level above it and mask.
3) Remove the mask at a lower subdive above level 0 and then move up one level. The mask should still be there.
4) Repeat 3) until you reach the highest subdiv level.