Geoserver CSS plugin - combining styles

I'm currently trying to write some SLD styles using the CSS plugin in geoserver. The problem is that the plugin merges single rules into complexed ones, ie. the following code generates 5 rules instead of 3 and the layer isn't rendering correctly. It all works ok when I use only one type of key, like define styles only for boundary or only for highway. I've found THIS, but I don't know how to understand it. Any ideas? Please help.

[highway = 'primary'][@scale<4000000]{
 stroke: black;
  width: 1px;
}

[boundary = 'administrative'] [admin_level = 2]{
    stroke: #B19AC2;
    stroke-width: 2px;
}


[boundary = 'administrative'] [admin_level = 4]{
    stroke: #B19AC2;
  stroke-width: 1px;
     stroke-dasharray: 3 2;
}

gives this:

    
  

    Default Styler
    
      Default Styler
      
        
          
            
              
                admin_level
                2

              
              
                boundary
                administrative
              
              
                highway
                primary
              
            

          
          4000000.0
          
            
              #B19AC2
              2
            
          
        
        

          
            
              
                admin_level
                4
              
              
                boundary
                administrative
              

              
                highway
                primary
              
            
          
          4000000.0
          
            
              #B19AC2

              3.0 2.0
            
          
        
        
          
            
              
                
                  admin_level

                  4
                
                
                  boundary
                  administrative
                
                
                  highway
                  primary
                

              
              
                
                  admin_level
                  2
                
                
                  boundary
                  administrative
                

                
                  highway
                  primary
                
              
              
                highway
                primary
              
            

          
          4000000.0
          
            
          
        
        
          
            
              

                boundary
                administrative
              
              
                admin_level
                2
              
            
          
          4000000.0

          
            
              #B19AC2
              2
            
          
        
        
          
            

              
                admin_level
                2
              
              
                boundary
                administrative
              
              
                highway

                primary
              
            
          
          4000000.0
          
            
              #B19AC2
              2
            

          
        
        
          
            
              
                admin_level
                4
              
              

                boundary
                administrative
              
            
          
          4000000.0
          
            
              #B19AC2
              3.0 2.0

            
          
        
        
          
            
              
                admin_level
                4
              

              
                boundary
                administrative
              
              
                highway
                primary
              
            
          

          4000000.0
          
            
              #B19AC2
              3.0 2.0
            
          
        
        first