I have been doing some research on the same topic, about categorising the parameters on the script tool dialog, and came across your message. I have tried your code in v.10 and it worked just fine. I think the problem was defining the right data datatype for your parameters. Here is the details:
- In the source .py file there are 4 params set by arcpy.GetParameterByText(x);
- In the script properties' Parameters tab, all parameters are set to String (This makes the difference I reckon);
- Only the first parameter has a Value List filter which contains the values of Point|Polygon|Line (w/o quotation);
When I run it, the script enables the right box among three given. If you are planning to use feature class as the first parameter instead of a string, you need to use Describe tool to access feature class properties in string format.
My problem was whether it is possible to set param.category property outside the getParameterInfo() def and the answer is that it is possible in initializeParameters(self).
Thanks,
Fatih