We have the same issue with OpenChannel hanging. In our case, we are trying to communicate with another powerbuilder app we built to handle custom print jobs.
In our scenario PB application 1 prints to PDF successfully (which causes splwow64.exe to run and it never completes). PB app1 successfully launches PB app #2 but when PB app #1 calls OpenChannel to start a warm DDE link to PB app # 2, PB app #1 hangs until we manually kill splwow64.exe. Then the openchannel completes, PB app #1 sends a print request to PB app #2 which successfully prints the job to PDF.
We tried the hotfix from microsoft (registry entry to set the # of seconds splwow64 waits after printing before closing) but it did not work. http://support.microsoft.com/kb/2815716