question regarding comboboxes in datagrid

[rsimlote]

I have a datagridview with 5 comboboxes. After selecting choices in the
first row, when the user move on to or enter into the combobox in the
next row, the selection from the previous row displays (as selected
value). The user assumes that as the selected value and may move on.
However once he leaves the combobox, the selectedindex is -1, and hence
nothing is selected.
I am still trying to figure out how can I set the selected value to -1,
when the user enters into the combobox.

Another question regarding textboxcolumns in datagridview. When the
user try to save the form without entering any value into the textbox,
my validation code gives an error message. Now when the user click back
in the textbox to type, the textbox is somehow allowing only 1
character to be entered. Somehow on every keystroke the text in the
textbox is being selected, and hence user is keep overwriting what he
had entered. Any suggestion on what i may be doing wrong, or what
handler do I need to fix this error.