passthrough example fails for source with large (>~70 files)

[sjamgade]

cargo run -p polyfuse-example-passthrough -- -s junk mnt
and in other terminal

➜  polyfuse git:(master) ls -1 junk | wc -l
0
➜  polyfuse git:(master) ls -1 mnt | wc -l
0
➜  polyfuse git:(master) for i in `seq 1 75`; do touch junk/test.$i.del ; done
➜  polyfuse git:(master) ✗ ls -1 mnt | wc -l
ls: reading directory 'mnt': Input/output error
0
➜  polyfuse git:(master) ✗ ls -1 junk | wc -l
75
➜  polyfuse git:(master) ✗ ls -1 mnt
ls: reading directory 'mnt': Input/output error

it also failed on the latest release with DEBUG handle_request{unique=896}: polyfuse_example_passthrough: errno=2 , any pointers ?

[sjamgade]

It would great to have some pointers on how/where to debug. I would happy to look into it