[Zope] zcatalog and versions

Can somenone briefly explain what exactly gets locked in zope 2.3,3's catalog when it tries to index an object which is hold in a version? The whole catalog? I found some answers which indicate that it has to do with the catalog when we see version lock errors where there shouldn't be any (from a naive pov), but I would like to know how far reaching these problems are, because when doing a rewrite of that application, I might be able to work around that. Do these problems still persist in zope 2.4.x? cheers, oliver