Automatic unindent does not always work

Reproduce:

1. Make new file

2. Set language to XML

3. Enter <test>

4. Press enter to move to next line (one or more times). At this point, the editor correctly indents.

5. Enter </test>

On step 5, the editor sometimes correctly un-indents, and sometimes does not. If it does not decrease the indent, removing the line and trying again is often successful.

I first encountered this issue with a custom language definition, but have now encountered it with XML as well. I first assumed it was a problem with my custom language, but I have not been able to identify the issue, and I have now see it with XML (which I have not customized at all).

This behavior was not encountered prior to build 2181. I have reproduced this on Sublime Text 2 build 2181 on Mac and Win64.