I was working on a plain-text document where I was making notes in the format:

431 Some title here
427 Another title
413

at which point Sublime decided I meant 431 again, leaving me with:

431 Some title here
427 Another title
431

and the key at that point stopped doing anything. Is there a way to turn off this behaviour, or do I have to use Shift+Tab each time instead? Thanks.

(edit: this is in build 3065 on Windows, in case it matters)

You can do this globally by adding the setting

"tab_completion": false

under Preferences…Settings - User

If you want to set it for a specific file type (say “plain text”) make sure you’re editing that type, then go Preferences…Settings - More and choose “Syntax specific - User”. This will open a file in to which you add the following:

{ "tab_completion": false }
Then save the file (which will be saved as, say, “Plain Text.sublime-settings” in your sublime user folder. Sublime will pick these settings up and override the defaults for specific syntax/file types.

Great, thanks!