When a knob is disabled programmatically, it does what it should: disables it and down-shades it colors. When it is re-enabled programmatically, it does enable it as it should but the colors remain down-shaded, which makes it look like it is still disabled even though it is not.
Your fix does indeed work. There is, however, a mistake in my post.
At first I thought that programmatically disabling and then re-enabling a knob was working, even though the re-colorization was not. I was wrong. Once it is re-enabled, certain features stop working correctly. Things like dragging the pointer around, or clicking on a label and expecting the progress bar to correctly change. The knob, and all of its attributes, acts really discombobulated.