Okay, I have now downloaded and installed the bzip plugin

Seems to me the viewer just does not support cell height, multiple lines in a cell, merged cells.
I think the results are like they are because the viewer cannot fit the text in a cell which is too small.
I have no clue which specification is supposed to be supported if any.
BTW. I have not much knowledge of the rtf format. You can find some information about rtf file
here. You can download a free viewer
here