Hi Nicolas,
So, if 1.4.x, 1.5.x, 1.6.x and 1.7.x are 'supported' versions, and some bug is found in 1.6.2, but turns out to be introduced in 1.5.1, we fix the bug in the 1.5 branch.
Then, if the bugfix is important enough, we merge 1.4 in 1.5 (which can be a no-op), 1.5 in 1.6, and 1.6 into 1.7. As such, every version branch 'contains' all 'older' branches.
I don't like this practise, because you certainly don't want to always incorprocate all commits of one release branch into an other. Just think about a hackish bug fix needed to be added in a former release, and in a newer release the problem has been solved in a completely different way, and now, if you have bad luck, the former release branch merges without conflicts into the new one, now getting the hackish fix into the new release, which might be even harmful. IMHO using cherry picking in this case is a lot better manageable. Greetings, Daniel