Running HP SIM 7.5 Update 1.
Adding a new node using "mxnode -a 1.2.3.4" completes very quickly (less than 5 seconds).
Adding a new node with the -w (wait) parameter (such as "mxnode -a 1.2.3.4 -w") takes a few minutes as expected.
I find that once I have used the -w parameter, all future runs of "mxnode -a 1.2.3.4" behave as if -w is specified by blocking until completed.
I found that I have to restart the "HP Systems Insight Manager" service to get "mxnode -a 1.2.3.4" behavior back to normal.