If you look at kdenlive's changelog for KDE Applications 15.08 and for KDE Applications 15.04.3 you'll see that "Fix autosave not working when opening project file from command line or click in file browser" shows up in both.
On the other hand if you have a look at gwenview, in 15.04.3 it shows "Make saving thumbnails work again" while it's not part of 15.08.
Does that mean that this bug got lost?
No, gwenview is actually the correct thing, we should not mention a bug again for 15.08 if it was released in 15.04.3, since well it's been released already :D
So why does kdenlive, marble and others show commits in the two places?
Because their developers are not doing the proper git-thing of commiting to the oldest supported branch and then merging up to master, so for git it's two different commits instead of the same (in case of the kdenlive commit in question it'd be https://quickgit.kde.org/?p=kdenlive.git&a=commit&h=cc55a9cea5c2f029744f8aba79a362fd302ec0bb and https://quickgit.kde.org/?p=kdenlive.git&a=commit&h=28b3cc7b5141fcc2fed84433b9fe9851c35b7e08).
Commiting the fix to the oldest supported branch and then merging up has lots of other benefits (like making sure you never forget a fix in master), but maybe this is the one that finally convinces more devs to switch to it, nicer changelogs ;)