Like theducks, I don't see the behavior you describe, so we need to look a bit more carefully at what you are doing that is different from what I am doing.
I am on Win7/32 using calibre 0.7.8+ (I run from source). I created a date column with yyyy-MMM-dd format.
1) Double-clicking on an empty cell gives me today's date in the right format. The descriptions below now apply.
2) Double-clicking on a cell containing a date opens the cell for editing. The year is highlighted. I type a 4-digit number, and the highlight moves to the month. I type a 3-letter month code, and the highlight moves to the day. I type one or two digits, hit return, and the date is set.
3) Double-clicking on a cell then using the mouse to move the cursor also works.
I tried following your procedures and failed. I am not allowed to type any letters after double-clicking on the day (number). I am not allowed to type more than 3 letters if I double-click on the month.
I do note that if I do not type all 4 digits of the year or all three letters of the month, the date reverts to what it was before. This happens because the underlying toolkit fails to parse the date.
Just in case you are referring to the metadata editor, I tried the same experiment there. I note that the date format is not respected (this is a bug), but after taking that into account, the behavior is the same as described above.
What are you doing that is different?
As for the popup calendar, after you open in, double-click on the year and set it appropriately. You can then set the month using the drop-down list. Then setting the day isn't quite so onerous.
