I reported this issue on bisect_ppx here first.

Basically what happened is that I needed to use both ppx_import and bisect_ppx on the same library resulting in a preprocess stanza looking like:

(preprocess
  (staged_pps
    ppx_import
    ...
    bisect_ppx -conditional
  )
)

This resulted in the library code always being instrumented. I assume the -conditional isn't properly passed somehow but I don't know much about the behaviour of staged_pps.

I suppose the fix for #57 will probably solve this issue but I can imagine a deeper preprocessor composition problem being involved here.

I'm as always happy to provide an example project and further detail as well as working on fix if needed!