But the question remains, why does it say (on my videos, at least) that it's "Building Preview" each time I try and preview past some transitions? Not all transitions, but on the ones where it does state this, it stubbornly refuses to ever let me preview that bit of the video in real time (I just hope, and review the final exported video).
I've found that once I've been editing for about 20 minutes (in which time I've probably got several dozen cross-fade transitions where I remove "Erm" and "Ums" and other such mutterings) this is when it all goes a bit "Building Preview" crazy. I've (sort of) learned to live with this constraint but it's still quite annoying. I've downgraded the preview resolution past the point where I can read any on printed matter, such as eBay listings (so that's not acceptable) but it made no difference anyway.
I realise that my graphics card is bottom of the list but there's no upgrade path for me there in my Ultra Small Form Factor PC. (sad face).