The "Scripting Syntax" section of the ArcGIS documentation should say "TRUE" should be passed for boolean parameters

[jjr8]

Apparently, when you call a script tool through the ArcGIS geoprocessor's COM Automation object, you cannot pass a VARIANT_BOOL to indicate True or False. Instead you must pass the case-insensitive string "TRUE" to indicate True or anything else to indicate False (including "FALSE", or even VARIANT_BOOL of True!)

I need to investigate further to determine if this only happens with Python (indicating an issue with pythoncom) or with other scripting languages (indicating that this is how the geoprocessor COM Automation object really works).

If this is really how the geoprocessor COM Automation object really works, the ArcGIS documentation should note this issue under the "Scripting Syntax" section, for all boolean parameters of all tools. The XSL should automatically insert a statement describing the situation.