This bug affects all races not only Mimot. (I have reported on another bug report the missing mining station icons for Mimot).
The upgrade (up) arrow shows on all stations that can be upgraded at the start of the turn.
Then when upgrade one station and nothing else can be upgraded, the up-arrow remains.
The same thing happens when I have upgrade all stations or only had resources for 1-2 stations. The up arrow is remaining there until the next turn for all stations.