I wonder if there is any side-effect of using something like the attached instead.
Your patch is better, so you have my OK. My original thought was to remove outside addPreview so that all MathHull (and other previewable insets) get their preview in this way (if preview empty, add snippet). I mean, buffer or bufferview should not have to worry about adding preview for insets. If some nested mathed is changed, it can simply remove this snippet so that it will be re-generated.... Anyway, your patch fixes this specific problem with less code, so it can go in. Cheers, Bo
