I think that's it, marria01. I went back to alpha3, tried to change the stereo separation (menu->sound->Stereo separation->ALl Tracks) and - guess what - I got the same sound as alpha 5. The change takes place few seconds after you actually click on the button to activate it.
In Alpha5, there's no way to switch it off, simply. That's my impression, at least, but to me it really seems that's what's happening.

Thanks for pointing this out, marria01.

So, now I think I am staying back with Alpha3. Unfortunately it locks so frequently...