Hello,
Just to keep this thread updated, we have found out that the issues is in the standard file FileUploader.js in version 1.28 that we are using currently because of SAP_BASIS version limitations.
The issue is fixed by SAP in all higher versions starting from release 1.30, but not in 1.28, even taking into account that 1.28 is still supported.
We have opened OpneUI5 ticket:
Kind Regards,
Siarhei