Deleting the last version of a document revert the document, but the revisions are mixed

1) create a new document, v1.1,
2) create a second revision v2.1,
3) try to delete the last version
=> it revert the document to 1.1, but keep a 2.1 revision

1) create a new document, v1.1,
2) create a second revision v2.1,
3) a third minor 2.2,
4) finally try to delete the last version
=> it create a new revision 3.1 with the content of 2.1