Wt

WPopuMenu::popup(WWidget *location, orientation = Orientation::Vertical) seems to reparent the menu to some layout container if the WTableView has a vertical scrollbar.
This just results in the horizontal scrollbar becoming added and the popup menu being invisible until that scrollbar is moved. Unacceptable UX.
(If the WTableView does not have a vertical scrollbar, the menu uses the full height of the screen, i.e. is not restricted to and hidden in a container. Good.)

CSS path without vscrollbar: html.Wt-layout body.Wt-layout.Wt-ltr div#ojansmv.Wt-domRoot ul#ojaovc7.Wt-popup.DevSwitching.dropdown-menu.wt-reparented
CSS path with vscrollbar: html.Wt-layout body.Wt-layout.Wt-ltr div#ojansmv.Wt-domRoot div#ojansmx div#ojansnz.SystemSummary div#ojanso0.Wt-stack div#ojaothf div#ojaovbc.Wt-itemview.Wt-tableview.DevSwitching.wt-fixedc1.unselectable div#ojaovbw div#ojaovbn.tcontainer ul#ojaovc7.Wt-popup.DevSwitching.dropdown-menu.wt-reparented