Pinch-to-zoom is not working

The pinch-to-zoom in/out is not working on sites. Although most sites are readable, this is causing a problem with sites that are using a map. For example:
www.prettigparkeren.nl
www.openstreetmap.org

The 'prettigparkeren' site is using a map from openstreetmap, so maybe other sites using a map from openstreetmap have the same issue. Pinch-to-zoom does work on Google Maps.