This is not a bug. In the 2D plot region x and t are special unknowns (abscissa and animation parameter); both are parsed as local variables (doesn't matter if there are these variables on the canvas as defined values - except for t that can be used if you don't animate the plot). Therefore when you write augment(x,y) you are trying to augment each x displayed in the plot with y.

Obviously you can define the input matrix before the plot, outside the region placeholder; in this case x and y are parsed outside the plot and the input is simply the 3x2 matrix.

The X-Y plot works differently.

Edited by user 20 May 2016 22:25:36(UTC)  | Reason: marked as solved

In general, only lastError [this variable will be overwritten by any function giving an error.] and maybe i (there should be a post by Martin Kraska somewhere about issues noticed using i in some special case) and e.