Think this is a known issue: https://success.salesforce.com/issues_view?id=a1p300000008ZL6AAM

Take a look and if this is the same problem mark that it affects you and I'll do the same.

Think this is a known issue: Bulk API with PK Chunking enabled throws ISE if contentType is application/xml, add support for application/xml

Summary
Bulk API query jobs with PK Chunking header fail, if the contentType is application/xml.

Error Message:
PKChunking failed. InvalidBatch : Wrong content-type for batch (text/csv), job is of type: application/xml "

...

Workaround
Set content-type for batch as text/csv