'Assignment made to the same variable' warning only happening when the variable isn't in an array

To reproduce:
1. Open attached project
2. Open the script "TheScriptToEndAllBugs.cs"
3. Notice that even though lines 9 and 12 both assign to itself (a[5] = a[5] and a2 = a2, respectively), only line 12 gives the warning "Assignment made to same variable; did you mean to assign something else?"