Lost Formatting

I hope i'm able to appropriately explain my problem.

I am creating a simple 'Holiday Request' form. I have managed to insert a drop down calendar, and am happy with the results.

However, each time i close the document, and return to it the next day, i find that the formatting for the calendar combo box changes. If i'm to use this form for easy employee use, it must hold it's formatting.

Anyone able to help? (This is one of 2 or 3 issues i'm trying to iron out, before i can roll out the new electronic form. I really appreciate any assistance!)