In QNX 6.3.2. sin consumes the entire data memory, if you start it with -l (looping) option.
You can observe it because sin lists every running process including himself in every cycle . The consumed data memory increases in every cycle, so after a while the OS runs out of memory. 
The source is available if you want to try fixing it yourself. Have you tried 6.4 maybe it’s already fixed.
I think using sin in QNX 6.>0 is not a good idea. I had worst problems than you. It hangs up when acting trough network in some cases… Why don’t you use just pidin?
Just tried it with pidin and its working ok. In 6.4 its fixed.