It saves just fine, everyone. Just hit the "resume" button at the bottom of the screen, instead of "start". I'll agree that isn't very intuitive, but hit resume.
I think I found a bug... when a gem is supposed to teleport back to the castle because of the undead spell allowing it to, it looks like it did, but when the enemies run over the (now empty) spot, they have the gem back and they are picking up right where they left off. It never actually teleported.
Its been posted before, and I have to agree... 1 mage with max power and chain on the high ground, 2 clerics to either side and 5 basic warriors is a good way to win. No restarts for me. Remember to either break their shield with another attack first, or hit archers first, when fighting warriors... it sucks to have all that DPS go down the tube on an 80% shield