If you are using v210(10-bit YUV422) files then they should be able to open fine. I believe BlueFish has their own 8-bit YUV packing scheme(at least they used to). The only other thing I can think of - is if BlueFish didn't put the scan type (progressive, interlaced) in the QuickTime Header then we default that it's a progressive file.
The files (at least SD) are fine to go back and forth with LH<->LS with two
exception: 1. 24-bit RGB/BGR is not supported on LS 2. 'R10k' or 'R10g' for QT and AVI as well as DPX/Cineom is not supported on LS.
We dont actually know if a Bluefish Premeire Pro Project will work inside a Xena project. It might, but we havent tested that here.