`prefer_system_check` succeeds for aliDoctor but fails for aliBuild?

[olantwin]

With 1.17.11 (but also 1.17.5), the following prefer_system_check works for aliDoctor, but fails for aliBuild:

prefer_system_check: |
    [ "$GENFIT_VERSION" = "$REQUESTED_VERSION" ] && true

Any idea what the issue could be? I pass --always-prefer-system to aliBuild, and replacing the check with true works for both aliDoctor and aliBuild.

From reading the code, I would expect exactly identical results...

The invocations of aliBuild/aliDoctor are:

aliBuild build FairShip --default release --always-prefer-system --config-dir shipdist

and

aliDoctor FairShip --default release --always-prefer-system --config shipdist

PS: I should experiment with the CVMFS remote stores, I somehow missed the recent releases...