When booting TC 2.6 rc4 I got an error when loading extensions:
mount: mounting /dev/loop27 on /tmp/tcloop/flash10 failed: Invalid argument occured while loading flash10.tcz
The boot continued and backup restored, but some of the extensions were not loaded.
The extensions load correctly under 2.5, and I had no problems running 2.6 with another set of extensions that doesn't include flash10.tcz.
edit: also did an appsaudit and sudo tce-update under 2.5, and as far as I can tell from this my extensions are up to date and have all needed dependencies.