Dry caramel 'curdles' when adding hot heavy cream I was making some caramel sauce today.
A simple recipe: 200g sugar (I used demerara), 500g cream (35% fat).
I dry caramelized the sugar under medium-low heat, stirring until all lumps dissolved and the caramel was all fluid and a deep amber.
At the same time, I heat the cream under low heat until it boiled.
I then combined both, slowly pouring the cream over the caramel in the pan (with the heat on low still on) while mixing vigorously with a whisk.

The thing is, at this point, the caramel on the edges of the pan 'curdled' -- and that was before all the cream got added.
It didn't crystallize into hard matter, but rather into thick, chewy, paste-like clumps.

I kept it on the heat, stirring and pressing these clumps against the bottom of the pan until they melted back into the sauce, and then added the remaining cream.
All the while, the mixture bubbled violently.

This has happened to me before, and I figured it might have been the temperature of the cream.
This time I was paying attention, so the cream was definitely hot and I am hence not really sure what the cause could be.


  Is this behavior 'normal', and it just takes some stirring under heat until it all comes together?


I remember making caramel sauce in large quantities at a restaurant in a similar fashion: dry caramelizing (granulated) sugar in the pan while stirring, then adding cream. 
The ratio of sugar to cream was even less (1:1 by weight), but I don't remember these lumps in the pan.

What we did in the occasion was pour part of the cream into the caramel while stirring; the caramel would bubble violently but eventually settle, at which point we'd stir in the rest of the cream.


  If this behavior is not normal (as I suspect), what could be causing it or how could I avoid it?
When havy cream is added after caramelizing the sugar, it's done to stop the caramelization process, keeping the desired caramel flavor and preventing the caramel from becoming bitter or even burning (if making caramel for sweets/pastry coating, the caramel is used as is and is cooled by placing the pot/saucepan in a cold water bath).

When adding cream to the caramel, using cold cream will rapidly cool your mixture, keeping the caramel at a temperature more suitable for a sauce, whereas using warm cream will keep the caramel closer to a softball temperature more suitable if you're making soft/chewy caramels, which could cause the edges of the caramel to thicken and start pulling together.

Since you brought the cream the a boil, your caramel probably hit the softball stage while you were stirring the two together. Try warming the cream to a lower temperature; the cooler the cream is, the more your mixture will bubble, but cooler cream will allow for a smoother caramel sauce and a larger margin for error to stay away from the softball stage.

Once you've hit the softball stage, your caramel will not be able to be stirred back into a sauce, you'll just have really soft chewy caramels, or you can heat them longer for harder chewy caramels (I highly recommend a candy thermometer at this point, or if you're particular about the density/chewiness of your soft caramels).