VS 2005 Combobox Hitting Enter Key Or Tab Key?

1. I type the first letter of the username i want in the combobox text area, the combobox drops down and shows me all the usernames starting with that letter. I scroll down to the name i want (as i scroll down, the text area holds each name but the SelectedIndexChanged event does not fire each time), then hit the Tab key, the SIC event fires and i get the result i want.

2. I do the same as above, but instead of hitting Tab key, i hit the Enter key. The same thing happens and i get the result i want.

3. This time, i first click on the dropdown arrow of the combobox such that it shows all usernames starting from the first name. I then type the first letter of the name i want. I saw that another drop down appeared in front of the first one and it was a smaller subset of names starting with the typed letter. I scroll down this smaller dropdown to the name i want (here also, as i scroll down, the text area holds each name, and the SIC event doesnt fire each time), then hit the Tab key, the SIC event fires and i get the result i want.

4. I do the same as #3, but this time i hit the Enter key instead of Tab key. But this time, the combobox text blanks out and the SIC event is not fired (although the name showed up just before i hit the Enter key). So i do not get any results back.