Noticed some of recent PCBs have come back from manufacturing with exposed copper on some vias. Looking at EasyEDA Pro, these vias have a setting for the solder mask expansion set to 'custom' 0 for both top and bottom. I have not set this.  If I select 'general', then back to 'custom', the fields then read -25.4 for both top and bottom, and the solder mask circle is removed. This a bug? I'd have thought by default vias should not have solder mask.