By entering custom or user dict flashcards modifying dictionary entries it seems to be possible to enter non printable data, e.g. HEX 09 = TAB - you do not see them, but they are there. If you export these flashcards as TXT files, the additional TABs destroy to some extent the resulting file: you either have the desired 3 entries per record (headword, pinyin, definition) or 4, when the "data-TAB" splits the definition into 2 parts.
I can clean the data file with a hex editor, but it would probably be a good idea to prevent non printable data in the "Edit Card" screen or erase HEX 09 from the data, when flashcards are exported to TXT files.