OK, I managed testing it in a more accurate way by setting mutation rates to 40 for veggies and letting them divide several times - they were mutating a lot in the original sim, but not when I loaded the save.
I can't test it in 2.4 as I don't have it. It's easy enough to test it, so I'll leave it for you, guys.
The 2.36.7 probably needs to be fixed though.
On a side note, I noticed another thing: when you load the saved sim, it does not automatically change all the settings. If you click on "new sim", the menu still has all the settings that were there before you loaded the sim. It is not really a bug, because one may argue that it's better that way... But I find it that it's more convenient for me to switch to the new settings. What do you guys think?