OpenXML: Text runs containing multiple text fragments + tabs lose content on merge

Testcase attached. This word file contains a slightly odd structure that more recent versions of Office may not produce any more (or it may be produced by LibreOffice or some other tool, I'm not sure). It has a run that contains multiple <w:t> fragments interspersed with <w:tab>. This is legal, but it breaks our filter. When you roundtrip this, the first "TEST" word is lost.

#!bash

tikal.sh -fc okf_openxml -x tabs.docx
tikal.sh -fc okf_openxml -m tabs.docx.xlf