@JamesStaddon, I would guess that the “mini-halos” that you mention are just one more thing that super-zooms don’t do well with. I don’t know for certain, but I’m guessing that’s just the best ‘bokeh’ you get in certain circumstances. Here’s an example that might show what I mean.
Tamron 18-270 Bokeh Example(Taken from this review of the lens….)