Command: *%comspec%
Parameters: /k
Start Path: %P
Okay, so there's actually three bugs here:
1) The start path is totally ignored, even if I enter D:\, when the command is to be started as an administrator (note the * before the command).
2) The %P variable is not expanded when used in Start Path.
You might think of another way to achieve the same thing, which is to pass the current directory as a cd command, Like so:
Parameters: /k "cd %P"
This is error-prone because of the quotes, and only works for directories on the C drive, because cmd.exe always starts at the user profile, which is usually on the C drive. So for this workaround, bug number three:
3) A variable for the current directory exists, but one for current drive is missing.
These problems lead me to think that achieving a button that starts an elevated command prompt at the current directory, is impossible. Please do corrct me if I'm wrong.
If there's a way to achieve this, please let me know. Otherwise this topic can remain a bug report

For reference, all this is tested on TC 9.0a x64 on Windows 10.
/edit
Okay, so this might work:
Parameters: /k "cd /d %P"
But that still leaves it error-prone because of the quotes. And bugs number 1 & 2 remain regardless.