If a Proxy is on the enemy team, and they plant a mine, it has a red glow. If teams then get shuffled, and the Proxy ends up being on your team, the mines keep their red glow instead of changing to blue.
EG I was just vs’ing a Proxy before and she had 2 mines down on the C4 plant site, and they shuffled the teams. She was then on my team but her mines still had a red glow for me and a blue glow for the enemy team. She eventually got 3 kills with her 2 mines because the enemy team thought they were friendly mines and just ran straight into them. Much rage was had after this as you can imagine.