title: Openlayers feature selection area is offset
body: <p>I have this very odd problem, where the selection box shifts further and further down the closer the marker is to the bottom of the map.</p>
  
  <p>If the marker is at the very top of the map the selection box is right on top of the marker, but if it's further down the map I have to click further and further under the marker to select it.</p>
  
  <p>Has anyone else experienced this? I'm using Openlayers 4.1.1. Here are some code chunks that could be relevant (I'm more than happy to share more code if that can help!):</p>
  
  <pre><code>    var imageStyleFunction = function (feature, resolution) {
          if (feature.iconSrc) {
              var anchorX = feature.anchorX ? feature.anchorX : 0.5;
              var anchorY = feature.anchorY ? feature.anchorY : 0.5;
              return [new ol.style.Style({
                  image: new ol.style.Icon({
                      src: feature.iconSrc,
                      anchor: [anchorX, anchorY]
                  })
              })];
          }
      };
  </code></pre>
  
  <p>...</p>
  
  <pre><code>    markerLayer = new ol.layer.Vector({
          source: new ol.source.Vector(),
          style: imageStyleFunction
      });
  </code></pre>
  
  <p>...</p>
  
  <pre><code>    selectionInteraction = new ol.interaction.Select({
          condition: ol.events.condition.click,
          //hitTolerance: 20,
          style: imageStyleFunction
      });
  
      selectionInteraction.on('select', function (e) {
          var userLocationFeature = _.find(e.target.getFeatures().getArray(),
          function (feature) {
              return feature.markerType === "userLocation";
          });
  
          if (userLocationFeature) {
              store.commit("setSelectedUserLocation", userLocationFeature);
          } else {
              store.commit("setSelectedUserLocation", null);
              selectionInteraction.getFeatures().clear();
          }
      });
  </code></pre>
  
  <p>...</p>
  
  <pre><code>function createMarker(location, iconFile, markerType, markerId) {
      var markerLayerSource = markerLayer.getSource();
      var markerFeature = new ol.Feature({
          geometry: new ol.geom.Point(transformLonLat(location.longitude, location.latitude))
      });
      markerFeature.iconSrc = app.config.map.iconPath + iconFile;
      if (markerType) {
          markerFeature.markerType = markerType;
      }
  
      if (markerId) {
          markerFeature.markerId = markerId;
      }
  
      markerLayerSource.addFeature(markerFeature);
  }
  </code></pre>