@Override
    boolean allowFocus(final Element element) {
        if (getTableHeadElement().isOrHasChild(element)) {
            return false;
        }
        return super.allowFocus(element);
    }
To fix issue gh-4684 we stop tables from taking focus if the user is clicking an item in the header.
This allows the header controls (filer text boxes) to take focus themselves.
stroom-core-client-widget/src/main/java/com/google/gwt/user/cellview/client/AbstractCellTable.java