do not pass model function into Parameters usersyms

lmfit/model.py

@@ -1861,7 +1861,7 @@ def loads(self, s, funcdefs=None, **kws):
         funcdefs : dict, optional
             Dictionary of custom function names and definitions.
         **kws : optional
-            Keyword arguments that are passed to `json.dumps`.
+            Keyword arguments that are passed to `json.loads`.
 
         Returns
         -------
@@ -1885,6 +1885,9 @@ def loads(self, s, funcdefs=None, **kws):
         self.model = _buildmodel(decode4js(modres['model']), funcdefs=funcdefs)
 
         # params
+        if funcdefs:
+            # Remove model function so as not pass it into the _asteval.symtable
+            funcdefs.pop(self.model.func.__name__, None)
         for target in ('params', 'init_params'):
             state = {'unique_symbols': modres['unique_symbols'], 'params': []}
             for parstate in modres['params']:

tests/test_model_saveload.py

@@ -254,8 +254,10 @@ def expr_func(x):
     result2 = ModelResult(model, Parameters())
     result2.loads(result1.dumps(), funcdefs={'mfunc': mfunc, 'expr_func': expr_func})
 
+    assert result1.userfcn == result2.userfcn
     assert result1.params == result2.params
     assert result1.init_params == result2.init_params
+    assert set(result1.params._asteval.symtable) == set(result2.params._asteval.symtable)
 
 
 def test_saveload_modelresult_eval_uncertainty():