SharePoint 2010 "Guardar sitio como plantilla" con campos de búsqueda en listas

When I try to save as a template (Site Settings -> Site Actions -> Save Site as Template) my SharePoint 2010 site, created with Visual Studio 2010, I get following error:

SPSolutionExporter: System.FormatException: Guid should contain 32 digits 
    with 4 dashes (xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx).
at System.Guid..ctor(String g)
at Microsoft.SharePoint.SPSolutionExporter.GetFieldSchemaXml(SPField field, 
    SPWeb web, Boolean isFieldFromWeb, Boolean removeSealedAttribute)
at Microsoft.SharePoint.SPSolutionExporter.ExportField(SPField field, SPWeb web)
at Microsoft.SharePoint.SPSolutionExporter.ExportFields
    (SPFieldCollection fields, String partitionName)

After intensive search I have found good artículo explaining what is going on wrong when SharePoint lists with lookup fields are saved in a template. Additional attribute "Overwrite="TRUE"" must be added in lookup fields definitions in Elements.xml y Schema.xml. After I did that I am able to save my site as a template. Very good.

However, lookups stopped working! No data from target lookup List are available now and even link to the same list (where some parent / child relations are specified) do not work anymore. Simply, such lookup columns now are always empty. "Add new item" dialog does not provide any data to specify in lookup column of new item. What could be wrong with attribute "Overwrite="TRUE""?

Gracias por adelantado,
Sal