Okay, today I updated both Headertabs and Page Forms to Master and suddenly it does not matter if Page Forms is enabled or not, the fault always appears.
To make a long story short, Page Forms has "nothing" to do with it (but I am not sure about this).
When you use Page Forms Master and Headertabs release 1_35 it works just fine.
The page now reports This page is using the deprecated ResourceLoader module "jquery.ui". Please use OOUI instead. but it works just fine.
I assume the move in Headertabs from jquery.ui to OOUI is somehow causing this problem after a page has been purged with &action=purge.
Maybe it has something to do with the fact that a &action=purge is now done with POST that needs to be confirmed.
I did find the items[i].toggle in the below js script.
For now the 1_35 version of Headertabs fixes the problem with an added bonus, we have our familiar blue tabs back :-)
OO.ui.StackLayout.prototype.updateHiddenState = function (items, selectedItem) {
var i,
len;
if (!this.continuous) {
for (i = 0, len = items.length; i < len; i++) {
if (!selectedItem || selectedItem !== items[i]) {
items[i].toggle(false);
items[i].$element.attr('aria-hidden', 'true');
}
}
if (selectedItem) {
selectedItem.toggle(true);
selectedItem.$element.removeAttr('aria-hidden');
}
}
};
