Working with shadow files means you are no longer playing the problem clip, just a low-res conversion of it.
It also means that with a large number of clips, you're having to wait around while the shadow clips are created, and for some reason that seems to take longer than one would expect as compared with the performance of MediaShow Espresso in doing conversions. It's intended for users whose PCs are simply not up to AVCHD replay at all. With the excellent performance of PD8 in replaying full HD AVCHD on a Cuda / quad core PC, it completely spoils the point of using PD8 in the first place to use shadow files.
I've spent so much time on playing around with every combination and permutation of possible fixes for this that I'm now seriously behind with many other matters, but I'm not particularly blaming Cyberlink for this type of clips not working happily in PD8 - so far I've only found one NLE which seems happy to handle it with no problems (problems in others range from similar freezes, or low fps playback, or flat refusal to play at all) - and that NLE is so simplistic that it doesn't provide a solution. However, it does show that it's possible to handle this format.
I did try converting the problem material AVCHD > AVCHD with MediaShow Espresso but then PD8 smart renders it with the known problem of jumping frames at transitions, so that doesn't work.
So for the time being all that can be done is to convert to full HD mpeg2 and work with that - and MediaShow Espresso does that very quickly, and the end result is very acceptable (to me at least). But it would be nice if one day this particular flavour of AVCHD would work natively in PD8. I'm pretty sure it's being looked at.