The interpolation of values incorrectly swallows too many errors. Specifically, when parsing the option's value during interpolation, any error gets discarded.
This is now fixed in commit 471558ea, released in version “1.2.0”.
Metadata Update from @bignose: - Issue status updated to: Closed (was: Open)
Metadata Update from @bignose: - Issue close_status updated to: Resolved