Override method in extended type

Hi All,
I have a type my_type_job.c3typ which extends BatchJob and it is defined in this way:

entity type my_type_job extends BatchJob<my_type_job, my_type_job_Spec, my_type_job_BatchValue> type key 'ML_TBJ' {
  UC: type_uc

  doStart: ~ js server
  processBatch: ~ js server
  allComplete: ~ js server

}

the start methods as following:

function doStart(job, options) {
  var uc = type_uc.fetch({filter: Filter.eq('id',job.uc.id)});
  if (useCases.count > 0) {
    var batches = _.map(uc.objs, function(ucs) {
      return my_type_job_BatchValue.make({UC: ucs});
    })
    job.scheduleBatches(batches);
  }
}

function processBatch(batch, job, options) {
	batch.UC.my_func(options)
}

my_type_job_BatchValue.c3typ is defined in this way:

type my_type_job_BatchValue{
  UC: type_uc
}

type_uc contains the method my_func declared in this way:

extendable entity type type_uc schema name "TGUC" {

my_func: member function(context: any) : any js server

}

and I also have type_uc_extended which extends type_uc and where I override my_func method:

entity type type_uc_extended extends type_uc type key "SBL" {

my_func: ~ js server

}

When I callmy_type_job.start(context) where my_type_job contains as UC a type_uc_extended type, it fails with this error :

EcmaError: TypeError: Cannot find function my_func in object **ID type_uc_extended **.

Someone can help me to fix this issue?

Thank you

@gdellefontane1 the start function is a member function.
try with

type_uc_extended.get("myjobid").my_func()