Windows 7 x64
Broken: 2.76b Official
No idea how long it's been like this, I can replicate going back to at least 2.73
Short description of error
Watch in wonderment as the sculpt brush and multires modifier cannibalize parts of the mesh.
Both seem to eat geometry on multires models. When applied to base, these changes create odd discontinuities in the base mesh that should be impossible to create otherwise. There would appear to be some kind of serious desync between the base mesh and the multires mesh that is unfixable by the user once it's appeared.
Exact steps for others to reproduce the error
Repeat the steps in the attached video with the test file.