Error with view "plain" when creating an app without tei_simplePrint.odd

I tested creating an app that uses other ODDs than the default ones (teipublisher.odd and tei_simplePrint.odd). It works fine unless for the "plain" view (via click on "single Page" in the tools menu).

This situation produces an error message:

err:XPTY0004 text()(
    ) is not a sub-type of element() [at line 52, column 55, source: /db/apps/matrix2/modules/lib/transform.xql]
In function:
	local:postprocess(node()*, element()?, xs:string) [52:13:/db/apps/matrix2/modules/lib/transform.xql]

The fix is to have an elementSpec for the TEI element in one of the app's ODDs:

<elementSpec ident="TEI" mode="change">
  <model behaviour="document"/>
</elementSpec>