I don't really know what you are referring to as a bug here?
I just run whatweb on my system and got the proper output beside some harmless warnings with ruby:
root@backbox:~# whatweb backbox.org
/usr/share/whatweb/lib/tld.rb:83: warning: duplicated key at line 83 ignored: "2nd_level_registration"
/usr/share/whatweb/lib/tld.rb:91: warning: duplicated key at line 91 ignored: "2nd_level_registration"
/usr/share/whatweb/lib/tld.rb:93: warning: duplicated key at line 93 ignored: "2nd_level_registration"
/usr/share/whatweb/plugins/wordpress.rb:436: warning: duplicated key at line 453 ignored: "2.7-beta1"
http://backbox.org [301] Apache, Country[UNITED STATES][US], HTTPServer[Apache], IP[192.210.141.229], RedirectLocation[https://backbox.org/], Title[301 Moved Permanently], UncommonHeaders[x-content-type-options], X-Frame-Options[SAMEORIGIN], X-XSS-Protection[1; mode=block]
https://backbox.org/ [200] Apache, Country[UNITED STATES][US], HTTPServer[Apache], IP[192.210.141.229], UncommonHeaders[x-content-type-options,strict-transport-security,x-mod-pagespeed], X-Frame-Options[SAMEORIGIN, SAMEORIGIN], X-XSS-Protection[1; mode=block, 1; mode=block]
root@backbox:~# cat /etc/issue
BackBox Linux 4.7 \n \l