WKT field not writable?

Hello, I created a new content type with an Openlayers WKT field. When I create a new node, I can indeed draw features (polylines, polygons, etc.) on the map and save them, but when I display the WKT field below the map and try to modify/add coordinates (while editing the node), these modifcations are never saved. Is this normal and how can I allow direct input of coordinates (polygons, polylines, etc.) in the WKT field? I have namely lists of coordinates (but not in GPX format) that I would like to add manually in my node, without using the map. How can I do this? Thanks for your help.