When using the Compare feature to compare branches, the comparison is actually always done against the common ancestor of both branches. Imagine the following example:

1. On master, a file contains 1
2. dev branches from master
3. On master, the file content is changed to 2
4. On dev the file content is changed to 3

When comparing dev to master, the comparison shows a change from 1 to 3. This is not clear from the UI, especially because the UI actually displays the ID of the latest commit to master in the UI ("User John Doe committed f77a3de2f3b yesterday").

The UI should clarify that the comparison is against the common ancestor, and should indicate what commit ID it is comparing to, instead of showing the ID of the last commit to the target branch.