Greetings, I have a boost ASIO application which is using deadline_timer for operation timeouts. It has been used for quite some time, but I have noticed some odd behavior with the timeout cancellation. The following is a brief description of the problem. First I initiate a connection request and setup a timeout timer set timer for 30 seconds async timer wait async connection request A couple of millseconds later the connection is up and in the callback I cancel the timer and start the next phase cancel timer start data activity... Most of the time the cancel is successful and I get the callback with operation canceled(as expected). But occasionally the cancel fails and returns 0 async operations effected, however this cannot be as the timer was created and is active (but not yet timed out)... then ~30 seconds later the timer goes off (and I treat it as a timeout). This occurs on average about 1 time per 20 connection attempts. The application is currently single threaded. Another developer has indicated that he has experienced similar issues. He is working on a completely different project with a different code base. The other developer worked around the issue by checking an internal state before propagating the timeout. I am loathed to do this, but have a similar work around in mind. Both the projects are building against version 1.39.0. I have done a diff between the latest version of boost and the 1.39.0 and did not spot any blaring fixes wrt deadline_timer. Has anyone else experienced this problem? Any patches/bug fixes in place for it? I am trying to reproduce this behavior consistently with some small sample code and have yet to do so. Thanks in advance for the help. Cheers Caleb