My second spin of a PCB I designed. I read about copper islands and kind of watched out for this. But my new boards have one flaw, where one region of copper fill (pour) became disconnected with ground. It was because a change I made, adding a via, caused that fill region to get isolated from ground due to a too-small area around the via. On my monitor, it is a very small sliver of copper left; in etching, it's an open circuit. Simple jumper wire fixes.
I might have caught this, using freeware expressPCB, had I clicked on the thing to highlight all pins in a net (ground) and had I noted that one pad, tied to ground, did not highlight as a member of the ground net.
Do costly professional packages find copper islands? To do so, it would have had to note that the sliver of copper was too small to assure etching wouldn't fail to leave continuity.