I discovered the 'Contains Words' bug when attempting once and for all to understand the difference between the various "Contains..." options. I think Adobe was trying to make it simple, but made it confusing and limiting instead.
Maybe the "Contains..." drop-down could be implemented as named regex presets, and Lightroom could ship with a set that implements the current ones for backward compatibility, but also the users could define their own.
Toss in a checkbox for "ignore case", and a better way of handling delimiters (e.g. specify delimiter explicitly, or have multiple lines instead of delimiters) and I'd be a lot happier.
-R