grid.column.filter.type = 'string'

src/controls/gridcolumn.js

@@ -7,7 +7,7 @@ export default function () {
     const ct = Ext.grid.column.Column.prototype.constructor
     Ext.grid.column.Column.override({
         constructor: function (config) {
-            const newConfig = _.defaultsDeep({}, config, column)
+            const newConfig = _.defaults({}, config, column)
             ct.call(this, newConfig)
         }
     });