Snippets (sometimes) trigger within snippets

Steps to reproduce: Create a new document and save it as "foo.rb". Type "def" and press tab. "def method_name ... end" appears, with method_name selected. Status bar says "11 characters selected - Field 1 of 2". So far so good. Type "foow" and press <tab>. Snippet triggers on the shortcut "w" and text is now "def fooattr_writer :attr_names ... end"
Note: when I ran through these steps again to reproduce it once more, it did NOT trigger within the snippet. However, subsequent tries DID reproduce the bug.
WIndows 7, ST2 Alpha 20110203