build failure with certain cowbuilder

I've got a build failure with freewnn via cowbuilder. However, same source can be built with pbuilder. And strangely, cowbuilder  in another host can build it.

• host + pbuilder = fine
• host + cowbuilder = fail
• host(chroot) + cowbuilder = fine
• host(old kernel) + cowbuilder = fine
• laptop + pbuilder = fine
• laptop + cowbuilder = fine
• virtualbox + cowbuilder = fine

... it's strange. What is the root cause of this?