So, exporting 73Kb ODS document (several sheets with one small table on each one of them) into XML in #LibreCalc results in 439Mb file.
#Vim basically dies on this file. #Emacs opens it instantly. I can even navigate it freely and syntax highlighting works. Although it doesn't help much.
Here's a catch:

me@desktop:~/temp$ wc -l file.xml
1 file.xml

It's a 439 Mb long line.
I have no idea what's wrong with LibreCalc.