>>>We thought it was our class, but then we threw a default Foxpro ComboBox on a form and set the RowSourceType to Fields, the RowSource to a cursor (tried a table also) and then started playing around with selecting different values. It is 2 column and we can consistently make it break. By choosing a row near the top of the list, then choosing one around number 250 in the list, it will not change the value. If we choose something near the bottom, it will. If we have one chosen at the bottom, then choose one near the top, it will not change the value. We are very tired of testing this, but it does seem to happen more when the display drops "Up" (near the bottom of the screen) then the normal "Down" direction. It seems to only happen when the cursor or table has (somewhere around) 250 records or more. Anyone seen this type of behavior?
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>>I've seen this behavior. Moreover, if you have many items disabled in the list, you would not be able to type a value to pick up the combo's value.
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>Is the only solution to have less than 250 or 512 or whatever? That can't be what other developers have chosen to do. Is there no workaround?

In most cases, anything larger than 20 or 50 items, 100 tops, is most probably not good for a simple combo - for ergonomic reasons. You may get better mileage out of an autofill combo (of which there are a few downloadable here), or from anything else that has incremental search which doesn't exactly catch Alzheimer after _dblclick seconds. Simple combo becomes just too long for a regular user and impedes usability.

I've had far better results with a textbox with a search term, enter, pop up a little form with a grid with matched records, select one, stuff back into textbox, next object.

YMMV, of course - my experience may be completely inapplicable in your case.