Desync when working with large lossless files

So, I have a MP4 Video file (captured with a Hauppauge Collossus, let's say), and I decide to use avconv to transcode it into a lossless Huffyuv AVI, since editing MP4 files is a massive strain on my computer. I transcode it and play the output file (80 GBs!), and it looks fine (in spite of avconv saying it lost a few frames). So I drag that into OpenShot to edit it. OpenShot's preview pane ends up showing my end result with a massive amount of audio desync, and the edited video OpenShot exports has the same desync. Is this normal? Anything I can do to avoid this?