vtkBlockColors appear incorrect

@patchett2002 @cory.quammen @pkf

When loading a vtm fileseries and showing vtkBlockColors, the colors will change over time unpredictably.

The way this multiblock dataset is set up is that there a block called mesh, which covers the whole mesh. The other blocks (HE, Cu, Steel, Air) are materials that are subsets of the mesh.

If all blocks are shown and vtkBlockColors are shown, the colors of blocks change over time. Or maybe the mesh block is being shown, randomly, it is hard to tell. If the mesh block is not shown (using Multi-Block Inspector), then the block colors are consistent.

Also, for this particular dataset, two blocks are the same color, sometimes.

There are also issues when only loading one vtm file. If one vtm file is loaded, you can still click on next timestep. When you do click on next timestep, vtkBlockColors will change.

Here is the dataset I am using: shapedcharge.zip

To reproduce: load the example dataset, click next timestep a couple of times. Go back to the first timestep, and step through time again.

Here are two images of what two different timesteps looks like when the mesh block is also shown: