Some more info about my save problems.
Game version: GOG.
System version Win XP with 4GB RAM or Win 7 with 8GB RAM (both, different computers).
Citation: "The Zero bytes savegame. When this problem happens, your game crash to desktop in the beginning of a battle and if you check it, you see a autosavegame with zero bytes or few kilobytes, at the end, a useless savegame. Other times, it does not happen when you load a battle and it happens when you try save a game and you see a message from the game speaking about if you have not enough space in the hard disk. Do not worry, you have space but the game can not write the savegame, probably because game engine can not write more amount of data.
Solutions? When it happens, you have not chances to fix it, but I know how the problem is because the code from the mod is too big. Based at my estimations, when xml code is bigger of 30mb, you can start to see the problem easily at big galactic conquest."
PR 12: config.meg is 39 mb
PR 21 demo: config.meg is 52 mb
No problem with save files in PR 12.
50% chance of problems in PR 21 (with precautions, saving only in quiet periods when fps is stable (27-28).
39-40+ mb is fairly safe.
More than 50 mb is probably not.
I don't know if others have this issue, though. Maybe with better PC (16-32 GB RAM?) and Steam version (aware of more RAM?) it can be avoided.