this is basically a forward of debian bug #826398 ( https://bugs.debian.org/826398 ), and the problem is that the indexer call table/interface structure in legacy_indexer.c doesn't line up with what indexer.h expects: the entry for openQfaState is missing, the wrong functions are invoked and eventually a null pointer is deref'd. the fix is a trivial one-liner.
thanks, i've added this in commit c1a7c09ef64644ccb658eb1d53d1e6d3c7047b55