This problem also happened with taxiway and runway.
(http://simutrans-germany.com/files/upload/z_slope.png)
The left one is also reproducible in underground.
Another problem.
I can up/down slope on a depot. (both on overground and underground)
(http://simutrans-germany.com/files/upload/z_slope2.png)
Solved in r2550. Thank you.
You can also apply the slope tool to flat bridge ends...
Did not work for me ...
It wasn't easy, but it worked somehow. I will prepare a 'tutorial' :D
Edit:
http://www-user.tu-chemnitz.de/~gerw/patches/pics/uslope8.png (http://www-user.tu-chemnitz.de/~gerw/patches/pics/uslope8.png)
should be fixed in 2572