You can confirm that it's running the proper detection check by searching the client's policy for the GUID of the detection check. Search for the detection check's name in the console in the top-right field, click on it, then use the GUID you find on the Properties page there.
The client policy is the .xml located at C:\Program Files\Altiris\Altiris Agent\Client Policies (or whatever drive you installed on). If the detection rule is changed and saved, the client's policy will be changed, and an update of the client policy will affect this .xml file.
If you find it has the correct rule but is not behaving as you expect, check out Joel Smith's article on Detection and Applicability rules:
https://www-secure.symantec.com/connect/articles/technical-white-paper-inventory-rules-detection-and-applicability-checks
If that doesn't solve it, feel free to post a screenshot of the detection here.