Lately, perhaps since upgrading to 1.31-wmf26, the "Undo" tag has automatically been added to edits when performing a rollback. If I'm not mistaken, this is not done on purpose, as only the "Rollback" tag should be added to edits that are rollbacks.

To reproduce:

1. Rollback any edit using the "rollback" link;
2. Whereas only one tag, which is "Rollback", should be added to your edit, the "Undo" tag is added as well.