Currently, Sailthru is experiencing issues with A/B campaigns using the third-party integration Taxi. When creating an A/B campaign, even though you may see both the A and B segments accurately in test, upon actual send segment A will be sent properly while segment B will be sent blank.
This incompatibility is being caused when the API import from taxi occurs, it doesn't use the necessary connection which would create/update a split campaign. This requires a different API.
You could get around this by importing the content into a single campaign, and then copying/pasting the code into a split campaign.
We can see how this was highly confusing, as our UI didn't make it clear that there was only content in the first version, and we're reviewing how this should be handled and are working to get a fix out.