When I create the Gerber plot file, the solder mask only covers the pads completely. It’s basically an inverse of what the solder mask should be. I’m using KiCad version 4.0.0-rc1-stable. To create the plot file, I go to File, Plot, select the layers I need and click on “Plot”. I use all defaults.
Normal behavior. No Panic. Your boardhouse expects them like that and wants them like that
Just make sure the solder mask retracts a bit (is bigger than the copper area that should be free) as there are always alignment ‘errors’ which if not factored in make your solder pads not big enough for a reliable solder joint. Your boardhouse has the variability listed under something like:
solder mask tolerance 4 mil (0.1 mm)… better shops do 2 mil (0.05 mm)
You adjust that setting global for your PCB (pcbnew > dimensions > pads mask clearance), per footprint (footprint editor > dimensions > pad setting) or per pad (pad properties either in pcbnew or footprint editor).
Personally I use the global settings and leave the others at 0.
For making the correct gerber settings for your board house search for ‘gerber’ or ‘gerbers’ here on these forums as the defaults might not be what they want/need.