Fix

label_studio/data_manager/functions.py

@@ -357,7 +357,7 @@ def preprocess_filter(_filter, *_):
     return _filter
 
 
-def preprocess_field_name(raw_field_name, only_undefined_field=False) -> Tuple[str, bool]:
+def preprocess_field_name(raw_field_name, project) -> Tuple[str, bool]:
     """Transform a field name (as specified in the datamanager views endpoint) to
     a django ORM field name. Also handle dotted accesses to task.data.
 
@@ -389,7 +389,9 @@ def preprocess_field_name(raw_field_name, only_undefined_field=False) -> Tuple[s
         field_name = field_name[1:]
 
     if field_name.startswith('data.'):
-        if only_undefined_field:
+        # process as $undefined$ only if real_name is from labeling config, not from task.data
+        real_name = field_name.replace('data.', '')
+        if project.only_undefined_field and real_name not in project.data_types.keys():
             field_name = f'data__{settings.DATA_UNDEFINED_NAME}'
         else:
             field_name = field_name.replace('data.', 'data__')

label_studio/projects/models.py

@@ -352,11 +352,14 @@ def one_object_in_label_config(self):
 
     @property
     def only_undefined_field(self):
-        """This property is true when there is only one column - $undefined$ - in this project.
-        This is useful for cases when labeling config has one field only (e.g. `image` or `text`)
-        and task data does not contain any other columns.
-        E.g. it allows to use data manager filters with `image` (or `text`) in the filter expression,
-        however, in fact task data does not contain `image` (or `text`) columns, it contains `$undefined$` only.
+        """This property is true when
+        1. there is only one object tag in labeling config,
+        2. there is only one common column for all tasks and it's $undefined$,
+
+        This is useful for cases when the labeling configuration has only one field,
+        such as `image` or `text`. For example, it allows to force a data manager
+        to filter `image` as `$undefined$`, because the task data, in reality,
+        does not contain `image`; it contains only `$undefined$`.
         """
         return (
             self.one_object_in_label_config