I got a bug report yesterday in which my package was broken because lexical scoping was suddenly in effect.

After some init-file-bisecting, this is the conclusion:

> It appears as though your first instinct about lexical-binding is correct. I had a ;;; -*- lexical-binding: t -*- directive in my init-packages.el file, which is responsible for downloading the installing missing packages (of which multiple-cursors.el is one).

>

> It seems that if the file which calls package-install has that flag turned on, it applies the lexical binding to the compiler, which results in the following compiler warning:

>

> In mc/region-strings:

> mc-mark-more.el:78:20:Warning: assignment to free variable `strings'

>

> This warning doesn't appear in the compiler messages if lexical-binding is nil.

This is on Emacs 24.2.1 on OS X. Full compiler warnings and code excerpts can be found here:

- Magnar Sveen