I am finding that if I customize an element's font (e.g. making its font weight bold), crtl+ scroll wheel will no longer affect its size. For illustrative purposes:
@settings
@font code
** keyword1_font_weight=bold **
Between the ** is the "body" content. The keyword group is, in fact, bold now, but the size will not grow and shrink with the rest of the text in the body pane.
Save, reload settings, scroll wheel no longer has any effect on the keyword1 group. Remove the setting above, and it begins working again.