[Secret History Spoilers] So what was the deal with

[soulcastJam he/him]

I'm not at all surprised that Sazed treats Kelser a little differently.

 

Kelsier is very charismatic and Sazed was used to following his lead, but there was this large period of time where Sazed lived without his influence.  He's out of the habit of listening to him.  Sazed has had intense personal struggles and his worldview has been flipped on it's head more than once, so he's changed a lot.  Add to that the realization the whole crew had that Kelsier had manipulated them into a plan he didn't share with them (a little loss of trust?).  Also that Kelsier wanted an entire class of people slaughtered while Sazed has seen how necessary they were to survival.  It's not really that surprising.

[DreamEternal]

Yes, it makes perfect sense for Sazed to distrust Kelsier. Even more if he read in the Spiritual connections of his shards the moments in which Kelsier punched their previous holders.

[Stormgate he/him]

Kelsier is more stubborn than a tree stump planted in Steelheart steel. If you give him even the tiniest chance of getting what he wants, he will tear apart Scadrial to get it. He almost did, actually. It was an accident, but still.