LatLonDocValuesField is used by LatLonPointSpatialField field type to store doc values. It does this by encoding the two double values into a long. If the field is part of a document which takes place within a atomic update operation RealTimeGetComponent is used to load the field values from the index.
If the request is a nested request (line number 654: isNestedRequest is set by DistributedUpdateProcessor to Resolution.ROOT_WITH_CHILDREN) all field values from the schema are copied into a SolrInputDocument (line 678).
The copy is implemented by toSolrInputDocument method (line 728 of RealTimeGetComponent). The method retrieves the FieldType of the SchemaField and calls the toObject method (line 740). In case of LatLonPointSpatialField type, when docValues is set to true and stored is set to false, the fieldData is stored by a LatLonDocValuesField instance.
The toObject method is implemented by the base class FieldType toExternal with the LatLonDocValuesField instance (line 373). In line 359 the method stringValue of the Field is called. The default implementation (line 259) checks if the fieldsData is either CharSequence or a Number and calls fieldsData.toString.
Because fieldsData is of type Long in LatLonDocValuesField class the value is not decoded correctly.
From my opinion LatLonDocValuesField must implement (override) the stringValue method and return the decoded value.