Update from older Snapshot to Milestone

Hello together,

I have SNAPshot openHAB 3.1.0 Build #2387 installed, is older as Milestone 5

if try to update (ubuntu 20.04 LTS) it doesn’t show the update (sources list for snapshot deactivated, repo for milestone activated)

while try to install with apt-get install openhab=3.1.0~M5-1

I allways get a warning M5 is older as Snapshot 2387.

Is this normal because of snapshot vs. Repo or is M5 really older?