What version are you running?
Review Board 2.0.18
What's the URL of the page containing the problem?
https://rb.corp.linkedin.com/r/744160/diff/2-3#6

Observe that ExternalAccountQuestionDetails shows as deleted even though QuestionDetails.pdsc did not change at all in revision 3.
What steps will reproduce the problem?

Modify files A, B, and C and submit to Review Board
Modify file B and update Review Board
Modify file C and update Review Board
Diff revision 3 and revision 2. 

What is the expected output? What do you see instead?
File B will show File Reverted and will display your changes on the left and the original version on the right which is very misleading. Instead, there should simply be no diff for File B. 
What operating system are you using? What browser?
Mac with Google Chrome 51.0.2704.106
Please provide any additional information below.