Unit movement bug
This issue (which only occurs in Red Alert, by the way) is actually related to the map you play on. It means the AI configured in the map is set to an IQ level higher than 0.
For skirmish maps, all Multiplayer players should be set to AI level 0. While the AI level generally doesn't affect the actual AI players in skirmish, it does affect the human players on the map; with the AI level set higher than 0, the game's AI will start controlling stuff owned by the player.
In its core, this is an issue in the map editor, since the editor has the wrong defaults set for the players; it defaults all players to IQ level 5.
If this is a map you made yourself, you should edit it and fix the issue. If not, you should alert the map's creator of this problem.
It's also advised to switch to the upgraded Mobius Map Editor, which does not have this issue, and will have these IQ values set to 0 on all newly created maps.
