Replacing feature geometry in Bentley MAP SS3

Hello

I have to port a SS2 Map application to SS3

In the application a feature has to get a new geometry, not modify.
The function I use works under SS2 but in SS3 it fails with shapes / group holes

I do this 

1 - remove the existing subfeatures

m_Feature.RemoveSubFeature(item);
GeoOperate.FeatureMgr.DeleteFeatureByUuid(App.ActiveDesignFile, item.Uuid, true);

2 - add the new geometry

BXFT.feature subFeature = GeoOperate.FeatureMgr.CreateFeature(item);
subFeature.Name = m_ComponentName;
subFeature.ApplyAttributeChanges();
m_Feature.AddSubFeature(subFeature);

m_Feature.ApplyAttributeChanges();

3 - write the feature (here the exception occurs)

m_feature.write(true)

The feature is locked before.

But what I am doing wrong?

Greeting Olaf