I'm on the current Steam version, playing with a nation mod.
Twice now, I have had a raider intercept battle generate, where I had an older cruiser (which was listed in the "X ship intercepts raider" event) plus a newer cruiser in a raider battle - and the newer cruiser had its maximum speed listed as the older cruiser's speed in battle. It's not weather limiting ship speed or mechanical breakdown - the ship's current and theoretical max speed are both listed as the lower value (in this case, 25 knots, compared to the 31 knots she should be able to make).
Screenshots of the division and ship status screens, showing Veneti with a listed speed of 25 knots:
- S1.png (43.29 KiB) Viewed 159 times
- S2.png (96.46 KiB) Viewed 159 times
- S3.png (73.31 KiB) Viewed 159 times