diff --git a/modules/plugin_dbui/converter.py b/modules/plugin_dbui/converter.py
index 4e1ca50e17f3da5f690a585393986ba45a0b6d2b..9ed655085305782bd634db076a6b3c5234319322 100644
--- a/modules/plugin_dbui/converter.py
+++ b/modules/plugin_dbui/converter.py
@@ -424,8 +424,13 @@ def to_gridFilter(table, **kwargs):
         # ignore composite field defined for form
         cfg = to_field(field, composite=False)
         
-        # remove default value 
-        # make no sense in this context
+        # remove field constraints making no sense for a filter
+        if 'allowBlank' in cfg:
+            cfg["allowBlank"] = True
+
+        if 'readOnly' in cfg:
+            cfg['readOnly'] = False
+                        
         if 'value' in cfg:
             del cfg['value']
 
@@ -433,6 +438,10 @@ def to_gridFilter(table, **kwargs):
         if cfg['xtype'] == 'xtextarea':
             cfg['xtype'] = 'xtextfield'
 
+        # replace all linkedcombobox by combobox
+        if cfg['xtype'] == 'xlinkedcombobox':
+            cfg['xtype'] = 'xcombobox'
+
         # empty text for combobox
         if cfg['xtype'] == 'xcombobox':
             cfg['emptyText']= T('select...')
@@ -440,7 +449,7 @@ def to_gridFilter(table, **kwargs):
         # prepare the name for the where close [table.field]
         cfg['name'] = name    
             
-        # store information to customize the filter
+        # store information to customise the filter
         cfg['filterComment'] = comment  
         cfg['filterOperator'] = operator
         cfg['filterType'] = field.type