Toolbar compound brush menu threw OutOfRangeException.

[Henry00IS]

It seems this anonymous lambda method will use the latest value of i which is 2 as the loop ended, not the current value at the time of the iteration.

It appears to be a Unity IL bug that causes "i" to be "2" in the lambda expression unless we assign it to a scoped variable.

[vertxxyz]

It's a C# behaviour in loops, not a Unity IL bug.
For loops and anonymous functions have had this issue and it's pretty widely known about.
C# 5.0 fixed the issue for foreach loops:
https://blogs.msdn.microsoft.com/ericlippert/2009/11/16/closing-over-the-loop-variable-part-two/

If you want to know more you can google: loop closure c#