importing table and IDs

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- i have a structure application where all elements have attribute "id"
- this attribute's type is set to "Unique ID" in edd

now:
when i open or import xml with a table, only elements "table", "thead", "tbody" and "tfooter" have set attribute "id", but for all other elements ("caption", "th", "td" and also all elements in table cells) this "id" attribute is empty

when i change the type of "id" attribute in edd to "String" everything goes well, but then i can't use cross-references in xml, because they need to point at elements which have a "Unique ID" attribute

does anybody know how to solve this and what is the cause of it

thank's very much for any help

acer