This is why documentation is so important :)
Editing the theme.yaml file is really finicky when opening it up and making edits because there isn't a lot of options available. You would think notepad is best suited but with trial and error and sitting here with my buddy to figure things out, we've made a discovery which should be put into documentation.
Opening up the yaml extension file in Dreamweaver will corrupt the file. The same with opening it in WordPad or even Notepad. My friend said he used notepad ++ which is an open source product that a lot of code developers use. I tried it and sure enough it worked well and it even has a save extension of "yml" but save it as "yaml" because with MT5, themes need the yaml version (with the "a" in it).
So... long story short, don't use html editors like frontpage, dreamweaver, wordpad, notepad, but use one like "notepad ++" for the yaml extension (and for any hand coding of proprietary extensions).
Reported on Movable Type 5
It's to do with the format other apps use for the newline character, and should be easily set within the app you are using.
That said I came to the same conclusion and just use notepad++ for editing yaml.
You can copy/paste an existing line and edit it, just so long as you don't insert a newline character directly in the app.
I owe my best bud for pointing out the notepad++ application. I think this will come in handy.
I would be willing to bed that the Windows version of DW uses CR LF. AFAIK the Mac version now defaults to Linux LF, which is what you need for YAML.
The bigger question is how the heck do I get syntax highlighting working. There is a RubyWeaver extention that ads YAML (among others like Ruby, of course) but it doesn't seem to work so hot on the Mac.
I know everybody and their brother likes TextMate, but I would just rather use DW, as I am using it anyways.
Emacs and any windows/Mac clones also do great job to edit this kind of programing file format. I use Carbon Emacs for my Mac :)