Tartanians, drowning and fleeing

[Saxon]

I got a few puzzling results last turn.

Is there a limit to how many Tartainians can be summoned in one game? Is there a reason I would fail to summon one two turns running? Can I get a refund of my twenty death gems? Ok, the first two questions are real, the third is just me whining.

Also, any reason units would drown suddenly, even though they have water breathing items and have been underwater for several turns already?

Finally, I thought troops that retreated from a siege were auto killed, even if there was a neighboring province to flee to. Is this correct? I am not whining about this, but some of my units successfully fled.