(Not a bug in wt itself but in the Widget Gallery.)
There are pages in the widget gallery that contain wrong links into the Wt reference:
It seems that most links into the chart namespace are wrong due to a missing namespace.
E.g. "CartesianChart" at the very top of https://www.webtoolkit.eu/widgets/graphics-charts/category-chart links to
The links on the other pages in the "Graphics and Charts" chapter are correct,
e.g. in https://www.webtoolkit.eu/widgets/graphics-charts/3d-numerical-chart
The working links have the namespace "Chart" in the link text. This is missing on the pages with wrong link targets.