I also came here looking for this.
To get around it I had to create a standard function outside of the script and call it with runtime.callFunction().
Something like:
* On function 'rotateTile'
* Parameter 'x' (Number)
* Parameter 'y' (Number)
* Parameter 'tile' (Number)
* Parameter 'rotateAngle' (Number)
----+ System: rotateAngle = 90
-----> shadowTilemap: Set tile (x, y) to tile tile (rotated 90°)
----+ System: rotateAngle = 180
-----> shadowTilemap: Set tile (x, y) to tile tile (rotated 180°)
----+ System: rotateAngle = 270
-----> shadowTilemap: Set tile (x, y) to tile tile (rotated 270°)