X6 bug? - Current cad layer keeps changing back after i set it

I upgraded to X6 on Wednesday and may not have my head around it yet, but what is happening is i click the 'CAD' (current cad layer) icon and set my cad layer. After a couple of minutes the current cad layer then reverts back to a layer i have called 'Driveway' I don't know if i'm setting the cad layer incorrectly or it's a bug. I'm finding it a little annoying that after i set the layer i can draw cad lines for a few minutes, then the current layer then changes to this layer.
No matter what layer i set it is always changing back to 'driveway' layer. I use the 'driveway' layer to draw the outline of my driveway in the site plan set.
Anyone else had this problem? Or am i doing something wrong setting my cad layer?

My guess is that you have an Anno set that is changing the current cad layer when you change to that anno set.

Thanks Glenn. Yes it was the default layer in my default annotation set.
I have not used annotation sets yet as I've only just started using Chief for construction set drawings.
I think I understand how anno sets work and will start using them now.
It didn't keep reverting to the default cad layer in X5 so that's what confused me.