Area Label Expression Length

Is there a limit to the length of an expression?
I am wondering this because of some difficulty I have had with my area label styles.

I have created a Lot Number expression that will not show up on my dwg, unless I edit the expression (not actually edit anything and select okay on the dialog box) then I have to regenall to get my labels to appear. But once I exit out of Civil 3D and open my dwg again I have to start the whole process all over again.

Sounds like a bug to me. Can you send me a copy of the file with the style and expression in it? I'll see if I can reproduce it on my computer.