If one installs features in the following order:

> feature:install odl-restconf
> feature:install odl-mdsal-apidocs

Then swagger UI produces 500 server error and karaf log contains:
2016-01-05 11:13:19,997 | ERROR | qtp369408453-100 | ContainerResponse | 71 - com.sun.jersey.jersey-server - 1.17.0 | Mapped exception to response: 500 (Internal Server Error)
javax.ws.rs.WebApplicationException: com.sun.jersey.api.MessageException: A message body writer for Java class org.opendaylight.netconf.sal.rest.doc.swagger.ResourceList, and Java type class org.opendaylight.netconf.sal.rest.doc.swagger.ResourceList, and MIME media type application/json was not found
at com.sun.jersey.spi.container.ContainerResponse.write(ContainerResponse.java:285)[71:com.sun.jersey.jersey-server:1.17.0]
at com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:1479)[71:com.sun.jersey.jersey-server:1.17.0]
at com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1391)[71:com.sun.jersey.jersey-server:1.17.0]
at com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1381)[71:com.sun.jersey.jersey-server:1.17.0]
at com.sun.jersey.spi.container.servlet.WebComponent.service(WebComponent.java:416)[199:com.sun.jersey.servlet:1.17.0]

Workaround is to install features on the same line:
> feature:install odl-restconf odl-mdsal-apidocs
OR
> feature:install odl-mdsal-apidocs
since that feature installs odl-restconf itself.

This is likely an issue with the jackson message body writer libraries.