color in raster image corrupted if ImageContext presents

[kswang1029]

To reproduce the issue:

1. open orion_12co_hera.fits
2. unset "recompute clips on new frame" and have -5 and 110 as the lower and upper bound in the colormap, respectively. Set clip to 100%
3. play the movie and the colors should be fine so far.
4. now replace the histogram panel by imageContext
5. play the movie again, now we should see a kind of clip level has been applied even through we have set the clip to 100%. And, when the movie plays, imageContext does not update accordingly. Keep the movie runs.
6. Now resize the panel of imageContext. We should see now the imageContext is updating. But, we should also see that the colors corrupted further. It looks like that the "recompute clips on new frame" is turned on again?