Hi Vladimir,
Try protocolcapture=file
Then file is stored in working application directory.
If it isn't working then something is wrong with the driver, but should work.
Also, can you create SAP Incident? If not, I can still report to engineering, just difficult to track since I am in Product Support and work off customers using SAP support. I have lots of stuff going on but could report this to Eng. I'd create an API test and then have you try it or review results so we can confirm it is same issue. I don't know if the ASYNC has anything to do with issue as I see same results with or without ASYNC enabled.
If not we can work via email (paul.vero@sap.com)
Cheers,
-Paul