This is as far as i know a vanilla bug:
https://cloud.githubusercontent.com/assets/2000703/17439442/6ecfbad2-5b28-11e6-8d77-01435175fcab.gif
Makes no sense for some of the buttons being usable shown above as the result can't be built.
You can use this piece to make banked straight descents though. WHilst they don't add anything to the game they can make a rollercoaster visually better.
@Gameinsky You haven't looked properly. This bug is about the game showing a button for a piece that does not exist.
Ah, fair enough.
This trackpiece exists and as far as I know it's buildable in OpenRCT. I had an issue where I had to go back to the vanilla game to build this piece because OpenRCT wouldn't let me, but that issue was gone after a few days so I guess it was just an error in that version of OpenRCT.
@Liampie Sigh... watch the video until the end and you'll see this is not about the 25-degree-down-to-banked-turn piece (for which the issue was #3361).
Still happens in v0.3.1
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@Gameinsky You haven't looked properly. This bug is about the game showing a button for a piece that does not exist.