Twitter actually shows a mention if it is preceded with any mixed
case of the characters "r" and "t".
https://twitter.com/sono_inf/statuses/310385896321056769 provides
a lower case example. Extracted streams from Gnip and Datasift
confirm this behavior as well.
This work done on the dime of: Simply Measured simplymeasured.com
Merge pull request #58 from kungfumike/master

Twitter actually shows a mention if it is preceded with any mixed