`drone exec` generates output folders owned by root

When launching drone exec under the working tree, it generates the output directory for generated files.
However, part of the directory, probably depending on how they are generated, are owned by root. My speculation is that files which are copied from somewhere in the source remain the original attributes, but files generated by the processes of root belong to root.

My question is, how can I specify the effective user, preferably the user who launchs drone exec, to run the build?

By the way, I am using Drone v0.4.

see https://github.com/drone/drone/issues/1492