Actually our program does not set them to 755 so that must be a server thing for you.
In image-inc.php they are set to 666
@chmod ($dst_file, 0666);
Note this is attempted since not all servers prevent chmod and I would assume on yours there are being set to server default of 755 by the server. In most cases where user's files are not set to 666 they are then defaulted to 644