I'm using trace_logf to customize what is printed in the Data column of the Trace Event Log view.
e.g. 

     trace_logf(800, "read %d of %d chars", rc, charsleft) 

prints something like

     "string read 5 of 10 chars" 

next to User Event 800.

Most of the time it works just like that, but in a couple of cases I find it refuses to print the
desired string - instead I get output more like what I usually see from a direct call to TraceEvent, 
e.g. "d0 1802270050 d1 1601071455".  

The only differences I can see between the ones that give me the expected output and the ones 
that don't is that they have different code numbers and are in different locations in the source code.

Any idea what might override the formatting in trace_logf?