"Diffs to ... from revision" feature does not work

"Diffs to ... from revision" feature does not seem to work. This feature is there at the point of adding content to a review, and we assumed it meant you can specify a particular base revision to diff to when adding files.

Our use case is generally code reviewing an entire development branch. Normally the add as "Diffs" works, but we've found crucible gets confused if the branch contains a merge from default in it as it thinks the branch contains the default chanegs that have been merged in. We thought the "Diffs to ..." feature would allow us to work round this by diffing to the last revision in default that the branch contains.
But when we try and do this we get an error like this:

Error
Server Error

Error 2
A java.lang.NullPointerException was encountered

Couln't find this revision with key src/main/java/com/ocado/atlas/inbound/business/AtlasPriority.java@9364fb16f1a4f5f4f8c33f51a259bfdce1b8d155 in repository CFC_InboundAtlasManager

How it is supposed to work:

• for every file that you add, instead of just adding that revision with the "diff to previous" (default behaviour), it will diff to the revision that you specified.

eg. say you have revisions 1, 3, 5, 10. If you add 10 normally, you will get a diff of 5-10. If you add 10 as "Diff to ..." 3, you will get a diff of 3-10.

What I would expect it to do if you chose "Diff to ..." 4, you will get a diff of 3-10. That is, the manifest version of the file at revision 4. This is where the NPE is occurring, and I have confirmed that this is a bug.