Basically, the fix for
MDL-21315 is pretty broken.
If a user is not using the fixed student column, and does not have the gradereport/user:view capability, then there is colspan, so the gradecelloffset horrible hack variable is being set incorrectly.
In addition the set_col function in grade/report/grader/functions.js is hard-coding row numbers like 2, and 3, but the number of header rows depends on the number of nested categories.
I'm working on a fix.