Hi Philipp,
Thank you for your interest in Syncfusion Products.
I am able to reproduce the issue in version 5.1.0.51. But this issue has been resolved in our latest version 5.2.0.25. Please upgrade to our latest version 5.2.0.25. You can get download link and unlock key details of v5.2.0.25 from below link:
http://www.syncfusion.com/support/Forums/message.aspx?&MessageID=68154Please note that version 5.2 of Essential PDF is a complete rewrite, so the APIs are not compatible with the previous version of Essential PDF. So kindly refer Syncfusion.Pdf.Legacy.Base.dll instead of Syncfusion.PDF.Base for maintaining compatibility and also your application should work without any problem.
Please try this and let me know if this helps.
Thanks,
Melba