No, that doesn't work -- running everything as an admin was one of the first things that I tried before posting here. But moreover, remember these 2 things:
1) As I mentioned in my original post, the AHK script DOES work for every other function EXCEPT text input. In other words, if it were just an admin-privileges thing, then the AHK script shouldn't function at all...excet that it DOES recognize commands to, for example, launch a program with a keyboard macro. The only commands it DOESN'T recognize are ones that command it to type text.
2) Secondly, I mentioned that I tried a second 3rd-party mouse button macro program, which produced exactly the same effect: I could create and run macros for any and all commands EXCEPT those that commanded a text input.
I posed this question in a different discussion forum, and a poster suggested that either my antivirus or HP bloatware that came preinstalled could be capturing / intercepting text-input, and suggested disabling my antivirus (I tried / didn't do anything)...but I don't know what HP bloatware he was referring to, so I don't even know what or where to disable it. Thoughts on whether this could be what's going on?