I started two more test games, and think I may have nailed down the problem.
I started a new game in 1.49 with the "Players Can Save Map" option on. Started the game, saved the map as soon as I found a world that showed a ruins description, saved the game, and quit. Opened the map in Map Editor 1.31, and finally saw the "combat movement" bug on that planet. Used the drop down menu to change it to "Ancient Ruins". Found another ruins world with the same bug, and put a Fixed Starting Point in that system, then saved the map.
Started a second new game and loaded the edited map. Picked a race that could colonize the second planet. When I started the game, the ruins planet showed as colonizable, but didn't show under Special, and colonizing the world did not find any ruins.
What I think is happening is that 1.49 is using a different identifying index for the Ancient Ruins ability than previous Versions did. When 1.49 sees the old Versions' Ancient Ruins number from a saved map, it misinterprets it as the Combat Movement ability, so it doesn't recognize that it's supposed to be a Special or give you Ruins tech.
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Cap'n Q
My first SE IV mod!
Hypermaze quadrant
The most merciful thing in the world, I think, is the inability of the
human mind to correlate all of its contents. We live on a placid
island of ignorance in the midst of black seas of infinity, and it was
not meant that we should go far. -- HP Lovecraft, "The Call of Cthulhu"