I'm using Aquamacs in markdown-mode with orgstruct-mode turned on.

When I start a numbered list:

1. foo

...at the end of that line, I want to automatically generate the next
number on the list, so I hit OPTION-RETURN

but instead of generating a "2. " on the next line, I get this error:

Debugger entered--Lisp error: (wrong-type-argument integer-or-marker-p nil)
  byte-code("\203

This used to work fine in markdown-mode with orgstruct-mode turned on...

Backtrace:

Debugger entered--Lisp error: (wrong-type-argument integer-or-marker-p nil)
  byte-code("\203