This is a known issue logged in our system under the internal reference number of SOC-3904.
Underscore is a wildcard character in one of the underlying expression parsers that we use here.
Unfortunately there is not currently a method to prevent the underscore from being treated as a wildcard.
There is an existing feature request you may want to vote for which would allow the underscore to be treated as a literal character.
http://redgate.uservoice.com/forums/390 ... rs-out-all
These forums are actively monitored by our development team and allow our users to request features and vote on them.
If a feature receives a significant amount of votes or is deemed to have merit development may include the feature in a future release.