I think the problem is with the Display Pattern you're using for the numeric field.
I'm guessing you picked a Display Pattern (on the Object palette's Field tab) of "$9,999.99". This type of pattern will always show exactly 6 digits. If there aren't 6, it'll replace the missing ones with zeros (0). If there are more than 6, it'll fill-in what it can and drop the rest (as you're seeing).
I believe you have two options: You can either add a bunch of "z" tokens prior to the "9"s to make the extra digits "conditional" or add a bunch of "Z" tokens to make them act as place-holders for missing digits.
The difference is this:
If you make your pattern "$zzz,zz9,999.99" and enter "123456" as the value, you'll get:
$123,456.00
If you make it "$ZZZ,ZZ9,999.99" and enter the same value, you'll get:
$ 123,456.00
Notice the 3 spaces at the beginning of the second option.
I've attached a sample form which demonstrates the two options using numeric fields with default values.
Stefan
Adobe Systems