Sizer Asserts in wxWidgets 3.1

When updating an existing application to wxWidgets 3.1, you may encounter new assertion failures in the code which seemed to work fine previously, with older wxWidgets versions. For example, a message box telling you that “only horizontal alignment flags can be used in vertical sizers” when adding an element to a wxBoxSizer or that “wxEXPAND flag will be overridden by alignment flags” when doing it with a wx(Flex)GridSizer might pop up where previously nothing was shown. What’s going on here and what should