Inserting a page break inside a table is currently not supported (the feature request is logged at https://feedback.telerik.com/Project/143/Feedback/Details/211108). Therefore, the Page Break button inside the Insert tab of the ribbon should be disabled when the caret is positioned inside a table.

Workaround: Track the position of the caret and when the latter goes into a table, set the Enabled property of InsertPageBreakCommand to false.