The finalized version of the SRFI-143 spec describes fxif as:

(fxif mask i j)

Semantically equivalent to bitwise-if. It can be implemented as (fxior (fxand (fxnot mask) i) (fxand mask j)).

It doesn't say the "SRFI-151" version of bitwise-if whereas other exports do. The expression above is not consistent with the SRFI-151 description of bitwise-if. The chibi test script included in the GIT repo for SRFI-143 tests for a SRFI-151 -style fxif.