Accordion Header Height

Using your example from the documentation:
http://webix.com/snippet/64e82666

Looks like ‘.webix_accordionitem_header’ should have line height adjusted to match? Or is this working as intended?

Yes, you need to modify line-height in .webix_accordionitem_header css:

http://webix.com/snippet/240d908f

or use Skin Builder with custom " Sizes → Bar height "