Just to add, don't get your users entering single-character codes such as V, S etc as some kind of fix - that really is not what users should be expected to interpret at all. You would be far better off placing your absence codes and their meanings in a small table which in turn can feed your combo instead of using a value list. I don't recommend using value lists at all in most cases, as how do you interpret the V or S or whatever when you go to report on it? You need to convert it back into Vacation, Sick etc, which if you used a reference table you could do automatically by joining the tables so that you always had the correct codes expanded to their correct meaning.
Can't say I've ever had the 'field too small' problem you are describing, however, and my concern would be that your database has been damaged and is suffering from corruption of the form concerned, given that it had been working OK for a time as you mentioned.
-Stewart