Planemo test denies having updated test data

When update_test_data flag is passed, the test data is updated as it should be. However, it wrongfully claims it has not updated anything.

planemo test datamash-transpose.xml --update_test_data
...
...
Shut down
supervisord has terminated
All 2 test(s) executed passed. Therefore, no test data were updated.
datamash_transpose (Test #1): passed
datamash_transpose (Test #2): passed

$ planemo --version
planemo, version 0.75.7