First textbox in a page via Html.TextboxFor has different size

Hi,
i have a little problem... I've even googled it but i came to no result
for every page, the first textbox control via
<%: Html.TextboxFor(m => m.XXX) %> 
has a different size, the rest ist everytime the same... only the first one is -huge-
help please on that DX 
...