Steps to reproduce
1. Open a new map after 1892
2. In the Water menu, select the Barge Canal Tunnel or Narrowboat Canal Tunnel tool.
3. Build a canal tunnel.
4. Add some locks to the canal tunnel.
5. Click on a flat tile in the canal tunnel.
6. Click on a lock in the canal tunnel.
7. Repeat step 6 many, many times.
Expected Results
A. The Narrowboat Canal Tunnel holds a Narrowboat Canal way.
B. The speed is the lowest of the the tunnel speed restriction, the way speed restriction, or the slope speed restriction.
C. The Way Info Window displays the correct information about B.
Actual Results
A. The Narrowboat Canal Tunnel holds the default water way, which seems to be the 'best' (fastest???) way, which after 1892 is the Large Ship Canal.
B. The Way Info Window mostly says that only the tunnel speed restriction applies (in this case 30km/h), even when the way speed or slope is lower.
C. But very occasionally it will show the slope speed restriction as applied.
Observations
This bug was found in the course of studying an earlier bug and there is relevant information in that thread (https://forum.simutrans.com/index.php?msg=210380).
I am not clear whether aspects B/C are issues with the actual speed restriction being applied or the Way Info Window. Testing is difficult because the canal tunnels have low height restrictions, which blocks most of the fast vehicles in pak128.Britain-Ex. That also means it's not easily exploitable across a lot of the timeline (but SimuTranslator doesn't seem to read the is_tall variable, so I can't think of a quick way to check whether it's totally impossible).
Aspect C is not consistently reproducible from step 7. I have tried a few different things (rotations, way types, canal types, with and without a vehicle in the lock) and I just can't work out why it very occasionally shows the speed restriction but mostly does not.
Aspect A also means that the Public Player can build underground rivers in canal tunnels. I doubt that's intended.