Hi all,
I finally got this dealt with... I think and hope. After my second message, telling them the problem again, assuring them I was not doing things I shouldn't with the boxes and asking them to try the search themselves... I got this response:
Dear Sarah,
We appreciate your message.
Well in that case, I am going to give you the number for our Family History Experts. They can walk you through the directions to make comments, corrections. For directions on the site, just hit the help tab by your username up at the very top, then type in "corrections". or 1-877-504-0905. Thanks.
If there is anything else with which we might assist you, please let us know.
Stacy
Member Solutions
Ancestry.com
So, it apparently needs a Family History Expert to replicate that search (JustJean and Sheila, take a bow!). I called the number, being tired of the fruitless back and forth with the help desk. Right away I got someone who checked, agreed, and called the programming department while I stayed on the line

Hoorah! He didn't know how long it would take them to fix it, but at least they now know...
Before calling I narrowed down the problem. Here's the scoop: It only affects
first name only searches (i.e. no surname, but anything else you would like to specify) on just the Scottish
1871 and
1891, the latest ones added. I checked all the others and they are fine. What you will get with a first name search is
all the people with someone of that name in their household. If you add a year of birth, place, occupation, etc., these will all apply to the person who comes up in the result, but that person can have any name at all, as long as they have someone in their household with the name specified on the search.
So, for example, search in the 1871 census for anyone named James ("exact matches only" checked) born in 1870 in aberdeen*, occupation: ag lab. You'd think the search would come up with no results, given the combination of age and profession, but no... you get three hits: Ann Cruickshank, Jemima Mutch and Alexander Ridd-- all born in 1870 in Aberdeenshire. One can imagine the wee things crawling out to the fields with their little farm implements and helping Dad

What they all have in common is that they all have an Ag Lab named James in the family.
Let's hope they clear it up quickly and that the new 1881 and 1901 censuses (coming "soon") will not have this glitch.
All the best,
Sarah