php - list() function returning strange filetype when the file size is big -

i'm dealing uploading images , have following php

list ($oldwidth, $oldheight, $type) = getimagesize($newimagelocation); 

to info file has been uploaded.

if upload file eg 37kb, contents of $type imagetype_jpeg

but if upload larger file, 2.5mb, contents of $type 2

i'm pretty sure filesize allowances ok , i'm struggling figure out reason happen. want enlighten me please :)

thanks