site:stage creates a strange directory structure in the case of multi module projects

The site:stage goal does not work properly on Linux in the case of multi
module projects, it has an annoying side effect. The command

mvn site:stage -PstagingDirectory=/home/user/staging

creates a strange directory structure under each module directory. After
the execution of the command I got the following directory structure:

child-dir/
home/
user/
projects/
parent/
...
src/
target/

Notice the home/user/projects/parent/... directory under child-dir/
(/home/user/projects/parent is the path of parent). The strange
directory structure contains no files.