drilldowns in IE

I routinely need to access forms in IE with extremely large drill-down menus. They are lists of hundreds (and in some cases a couple thousand) items in alphabetical order. If I start to type while in the field, the system will drill to the appropriate selection. The menus work fine from my office, but on my home PC, they do not - I can only drill to the first letter. Same version of Explorer, and all the settings are the same. I have searched high and low to find how to get the drill downs to work on my home PC, but cannot find the setting. Any ideas?