If is difficult to answer you with this heterogenous extract from sequence files. Nevertheless, it seems that the sequence file size increase because of the modifications that are made in the sequence file : properties are set to non default values, descriptions and variables that are added, etc... After looking at your text files, all the data seem to be usefull. A good way to know what are the differences between to sequence files is to use "Diff Sequence File With..." from the "Edit" menu.
If you have two sequence files with the same behavior and with different sizes, please attach the whole files to this thread. I will take a look at them.