MendixIdentifier cannot be cast to java.lang.String after upgrade 7.7.1 to 7.8

I found an issue in a datagrid that contains a columns from a [*-*] relation. 

Does anybody has an idea how to avoid this issue in Mendix 4.8.0, because it was working in 4.7.1 and before?

The corresponding error message is:

java.lang.ClassCastException: com.mendix.basis.objectmanagement.MendixIdentifier cannot be cast to java.lang.String
    at com.mendix.webui.jsonserialization.ResultSerializer$$anonfun$generateMap$1.apply(ResultSerializer.scala:85)
    at com.mendix.webui.jsonserialization.ResultSerializer$$anonfun$generateMap$1.apply(ResultSerializer.scala:85)
    at scala.collection.immutable.Map$Map2.foreach(Map.scala:137)
    at com.mendix.webui.jsonserialization.ResultSerializer.generateMap(ResultSerializer.scala:85)
    at com.mendix.webui.jsonserialization.ResultSerializer.com$mendix$webui$jsonserialization$ResultSerializer$$generate(ResultSerializer.scala:73)
    at com.mendix.webui.jsonserialization.ResultSerializer.generate(ResultSerializer.scala:60)
    at com.mendix.webui.jsonserialization.ResultSerializer$$anonfun$generateMap$1.apply(ResultSerializer.scala:85)
    at com.mendix.webui.jsonserialization.ResultSerializer$$anonfun$generateMap$1.apply(ResultSerializer.scala:85)
    at scala.collection.immutable.HashMap$HashMap1.foreach(HashMap.scala:221)
    at scala.collection.immutable.HashMap$HashTrieMap.foreach(HashMap.scala:428)
    at com.mendix.webui.jsonserialization.ResultSerializer.generateMap(ResultSerializer.scala:85)
    at com.mendix.webui.jsonserialization.ResultSerializer.com$mendix$webui$jsonserialization$ResultSerializer$$generate(ResultSerializer.scala:73)