Sometimes the acreage search on the consumer side of HAR is not very user friendly, and doesn't alway give you the desired results. I just tried it myself and verified what you said, so I don't think you are doing anything wrong. If you would like, I can set you up on a search from the Realtor side and email you what I find - no strings attached, and you can contact me if you see something that works for you.
Judy Regil, Keller Williams Realty, jregil49@msn.com

Are you using http://www.har.com ? This is the Houston Association of Realtors website. It will have everything on the MLS from Galveston to Huntsville. Of course, I will be happy to search for you. I specialize in Montgomery County.

Thank you,
Julie Young
Keller Williams Realty
281-734-4846
jayoung@kw.com