diff against other revisions does nothing

Hi,

Maybe I am doing something wrong, but lets say the tip is on r99, and I browse through the repository on bitbucket, click on a file, then I see what appears to be my file showing the diff with the last change, say r54. Now I want to see what happened between this latest file r99 and a really old version r28. I click on drop down box and select r28, then click on diff. At this point, I see exactly the same page, i.e., the r99 diff with r54. I can do this r99 diff against r28 from command line, but it does not work on bitbucket.

Am I doing something wrong or is this a bug?

thanks