There is a bug when turning on V1.1 compatibility in Prestashop V1.2
You will get javascript errors that will mess up the functionality of the page (attributes, ajax cart and possibly more) Error: syntax error extraParams:{ajaxSearch:1,id_lang:}
Error:
syntax error var displayPrice = ;
To fix this you need to add 2 new lines in /init.php below line #180, it should look like
'currencies' => Currency::getCurrencies(), 'priceDisplay' => intval(Configuration::get('PS_PRICE_DISPLAY')), 'cookie' => $cookie, 'id_currency_cookie' => intval($currency->id),