I just realised that the name of a property gets "renamed" and is thus listed as a wanted property after the entry of an invalid property value. The normal behaviour would be to throw a message that the property value is not valid. This happens if the property value starts with a colon, e.g. ":0049 30 12345678" as a value for the property "Ruf" would result in a wanted property "Ruf:" with the value "0049 30 12345678". Additionally the value gets displayed like a property value of datatyp page though the defined datatype of the property "Ruf" is telephone number. The same happens to datatype quantity and temperature. I have recreated this at scratchy: http://scratchpad.referata.com/wiki/Ruf
MW 1.17.0 and SMW 1.5.6 or SMW 1.6.1, probably happening to SMW 1.6.0 and SMW <1.5.6 though not tested.