I hate to say this but my opinion of pressed wood, particle board and any sawdust and glue product, it does not belong on a home. This stuff bloats up like a ballon when in contact with water.
if you are pondering the idea of siding, I would suggest that you do this. this stuff will be a night mare for you as long as it stays there.
First, the paint is having a problem adhering to the stuff because of the glue and its shiny properties. Nothing can penetrate the outside skin to allow paint to stick. Then if you chip the stuff or break the skin it will go to pot.
please consider another alternative besides any more paint. It just wont work for you.