I have created a new hugo site and I observed one behaviour with hugo v0.15.

1. I have a theme which doesn't have a static folder
2. The site uses that theme
3. Site has a static folder
4. hugo create public directory with the content except the content inside of "static" folder. It happens with server command too.

My current workaround is to create an empty "static" folder in the theme directory and then hugo copy the content inside of "static" into the "public" directory (or the specified output directory) as expected.