I noticed a strange thing when debugging my tool.
There is a / missing, so the directory structure gets screwed up and there is unwanted behaviour like left-over tmp directories.

Example

output files:
/tmp/tmp4NvYcRfiles/000/dataset_10.dat
/tmp/tmp4NvYcRfiles/000/dataset_11.dat
current working dir:
/tmp/tmp4NvYcR/job_working_directory/000/9

where /tmp/tmp4NvYcR/galaxy-central-master/ is the tmp Galaxy root.
tmp4NvYcRfiles should (obviously?) be tmp4NvYcR/files/

Is this a bug in Galaxy or planemo?