`rebuild` prints out the same error twice

[yichengq]

yicheng.qin@yicheng ~> cat hello.re                                                               10
let myVar = "Hello";

print_endline | 1;

yicheng.qin@yicheng ~> rebuild hello.native
+ /Users/yicheng.qin/.opam/4.02.3/bin/ocamldep.opt -modules -pp refmt -impl hello.re | tee hello.re.depends > hello.ml.depends
File "hello.re", line 3, characters 14-15:
Error: 1818: Incomplete statement. Did you forget a ";"?

File "hello.re", line 1:
Error: Error while running external preprocessor
Command line: refmt 'hello.re' > /var/folders/34/4yx9dw4x037_7j6dwtztmw440000gn/T/ocamlpp016c49

+ env OCAMLC="ocamlc.opt" /Users/yicheng.qin/.opam/4.02.3/bin/rec -c -pp refmt -o hello.cmo -intf-suffix .rei -impl hello.re
File "hello.re", line 3, characters 14-15:
Error: 1818: Incomplete statement. Did you forget a ";"?

File "hello.re", line 1:
Error: Error while running external preprocessor
Command line: refmt 'hello.re' > /var/folders/34/4yx9dw4x037_7j6dwtztmw440000gn/T/ocamlpp356bfc

Command exited with code 2.
Compilation unsuccessful after building 2 targets (0 cached) in 00:00:00.

This reads really verbose.