After deep investigation I found that
this works in libre office <row r="1" spans="1:1" ht="15.00" but this doesn't <row r="1" spans="1:1" ht="15"
Based on the spec it is bug in libre office. But I will try to fix it with "15.00" which works also in ms excel.
Until the fix is propagated, you could try to increase a height so the row is not exactly 15.