I have no idea what what your repo maintainer changed when packaging v0.9.0 for Debian/sid, but I do know that the current Flightcrew plugin works fine when Sigil v0.9.0 is built from source (with either Python2.7 or Python3.4).
And building from source is currently the only "officially" supported method of installing Sigil on Linux. As much as we might like to, we can't really work on bugs that someone else may have introduced. You'll probably need to report this to the Debian/sid repo maintainers.
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