In Page_Load of an EPiServer page, I am replacing some [[content]] with some data from a database using this code:

if (!PageEditing.PageIsInEditMode)
{
if (property.InnerProperty != null)
{
var prop = property.InnerProperty.CreateWritableClone();
string webFieldContent = contentData.GetWebFieldContent(propertyName);
prop.Value = webFieldContent;

property.InnerProperty = prop;
}
}

This works fine on the page itself, but not on local blocks. When debugging, i can see the data replacement being done as expected, but hwen the page has loaded, the [[content]] has not been replaced after all. Does anyone have an idea why this happens - or even better - what I can do to make it work?