Yes, if anyone of them is off, saving was OK.
However, today, I reinstalled windows 10 on my computer. I installed English version of the system! And, suddenly, there is no saving bug.
So, although I am not sure, there might be some incompatibility between Wavelab and the Czech Windows 10 which I was using before. However, it is gone from my computer, so, I cannot make any further investigations. I will never return to Czech Windows again, as it was stressed so many times, use only the English version of the system for serious audio work. I ignored this warning up to now, but there may be good reasons not to.
So, now Wavelab was running OK on the English Windows 10.