Thanks for the very useful feedback!
I already found the berserker and repair bugs, they have been fixed. I'll have to look into the sound issues - is it only the sound effects or also the music? Does it occur mostly in "crowded" moments when there are a lot of microbes around and a lot of action going on? Could you check the pndrun_microbes.out for buffer underruns? It could be that the game is just taking too much cpu to prevent the sound from keeping up, causing buffer underruns. If those are the problem, things should be better in the new SZ1.51 and in the new version which will do frame dropping if needed and uses some NEONized code from notaz to make rendering more efficient.
The energy bonus transfer (1/4th of the remaining energy gets added to the starting energy of the next level) is supposed to be a feature, not a bug

- the idea is that you get rewarded for playing levels in a row versus doing lots of restarts. It is trivial to change this if you think it is a bad idea - also perhaps the bonus should scale down in higher difficulty settings.
Your feature requests are good, I'll try to implement as many as possible.
It looks like you playtested quite well, you have discovered quite a few tactics, like healer placement: yes, their target selection is kind of basic: whatever is in range and needs healing, top-to-bottom left-to-right first, which gives quite unbalanced healing. Maybe I could add another upgrade for the healers to do smart healing, i.e. lowest hp first.
There will be a 3 seconds delay before the first wave starts coming. I could make it shorter in higher difficulty settings.
I've tried Insane until "Microbes" level 4 succesfully, however this is on my current version which has slightly different unit balance.
Nanobots is a cool idea, but perhaps as additional units, because the current units already refer to the human immune system (in names and graphics), and I don't want to throw that away. I'm not too worried about things not making sense - it's just a game after all, and to make it biologically/technologically accurate would be impossible and would probably take the fun out of it.