Thanks for the suggestion, Tommy. That would solve the problem, since it functions sort of like the pull-down menu which pops on that field - another, if lesser, annoyance of mine, since I type faster than it loads, so, not infrequently, I hit return and it saves some random explanation into the field instead of what I typed. I use something similar for the bibliographic references I use frequently.
But using a work-around avoids the issue of why the field is set up this way in the first place. I'd really like an explanation and, if at all possible, a way to turn it off.