meta property "dcterms:modified" changed

[outsideMyBox]

Hi,
I tried to load an existing epub and save it again. Unfortunately the generated epub contains errors when tested with epubcheck
Amongst them:

ERROR(RSC-005): /OEBPS/content.opf(-1,-1): Error while parsing file 'The prefix "dcterms" for element "dcterms:modified" is not bound.'.

epublib modified the original line:
<meta property="dcterms:modified">2015-05-02T11:44:00Z</meta>
to
<dcterms:modified>2015-05-02T11:44:00Z</dcterms:modified>
After a bit of digging out I found that PackageDocumentMetadataReader.readOtherProperties() saves it as an 'otherProperties' and PackageDocumentMetadataWriter.writeMetaData() writes it using the property as the tag name.
Is it a bug or is it the normal behaviour? At least it should be the case for dcterms:modified.

[Richie94]

@outsideMyBox Just curious if its same for you: was it an epub3 file?