Launcher overwrites downloaded snapshots

Hello!

I downloaded the MC 15w34a snapshot, then I downloaded the 15w34b snapshot when it came out.
I wanted to delete the folder of 15w34a in '.minecraft\versions', then I saw that the launcher deleted the 15w34a folder and replaced it with 15w34b.
I downloaded an older 1.9 snapshot, took a look at the versions folder again and I saw that the launcher replaced 15w34b's folder with the older snapshot's folder.

If this is meant to be a feature, or someone already reported this bug (and I didn't found it with search), I'm sorry...