There seems to be a bug when creating a DriveTrain/SmartDrive object with the optional arguments in INCHES. No errors, but both drive_for and turn_for methods do not work properly. When using MM units everything works as expected, even drive_for with INCHES.
Looks like an issue (ok, a bug) with Python code,.
C++ is probably ok, blocks only create a drivetrain object using mm (you can specify inches but it converts internally).
We have no updates planned for the near future but it should be fixed in the next release.