scala debug - how to step into the 2nd method when there are 2 methods in a line?

In the following line :
                     vm.foreach(this.nature_+=(_,pred))

I want to step into the method nature_+=(). So when it first runs to this line, I press F7, then 'foreach' become highlighted pink

Then I try to click on 'nature_+=', press right arrow, then press F7 again, but I CANNOT step into the 2nd method 'nature_+=' ANYWAY, just step into the 1st method, can NEVER step into 2nd method!!!

So, how can I step into the 2nd method when there are multiple methods in a line? This is very common in scala, moreover, in the previous version of scala plugin, I can do this!!!