GDS Text format is not always maintained - if you just click save, the file is saved as binary. For example: save a layout as "GDS/text" with extension "gdstxt". It will become a text file. When loading that file and saving again, it is made binary.

Furthermore, when using "Save As", the GDS option panel vanishes when "GDS text" is selected as format. However, these options are basically available, but cannot be used.