Path with dot results in confusing build error about oasis HOT 2 OPEN

$ grep libextunix_stubs _log
# Target: src/extunix_stubs, tags: { annot, bin_annot, c, debug, extension:a, file:src/libextunix_stubs.a, my_warnings, ocamlmklib, quiet, safe_string, traverse }
              - Building ./src/libextunix_stubs.a:
                      - Building ./src/libextunix_stubs.cmx:
                              - Building ./src/libextunix_stubs.ml:
                                      - Building ./src/libextunix_stubs.mly
                                      - Building ./src/libextunix_stubs.mll
                              - Building ./src/libextunix_stubs.mlpack
                      - Building ./src/libextunix_stubs.mllib
                      - Building ./src/libextunix_stubs.clib:

E: Failure("Command ''/home/ygrek/.opam/4.05.0/bin/ocamlbuild' ./src/libextunix_stubs.a ./src/dllextunix_stubs.so ./src/extunix.cma ./src/extunix.cmxa ./src/extunix.a ./src/extunix.cmxs -tag debug' terminated with error code 6")