When using the style editor to edit and preview an MBStyle, changes are sometimes not reflected in the underlying SLD file.
This seems to only occur when "Preview as Style Group" is enabled, and when the (initial) preview layer is different from the layer referenced in the style group.
Additionally, it only seems to happen when certain properties are modified; sometimes the SLD is updated just fine. I have been able to reproduce it when changing "icon-size".
Trying to use a function for icon-size has no effect.
Looking at the generated SLD, it appears this is because the icon-size is passed in as embedded CQL:
We should be able to just pass in the icon, and use the size parameter of the point symbolizer here.