I have a conditional parallel that works on a two different sections of a document at once.

I have a workflow called city splitter that I use as a shortcut to split apart City, ST, zip that does some simple validations and such before returning functions. 

when I invoke that workflow on both sides of the parallel it canceled whichever invoked workflow started second (usually within milliseconds of each other).  

It took me a while to determine what was going on but it was the fact that the invoked workflow was trying to return invalid data. The invoked workflow was returning "no" for a boolean value. As soon as I fixed this it started working correctly and running both workflows fine.

I didn't see any errors in the invoked workflow or in the log for that invoked workflow. I only saw an error in a conditional on the original invoking workflow that tried to parse that boolean AFTER the invoke workflow finished. Whichever workflow started 2nd would finish (when looking at it in search results/log) but would show up as canceled in that workflow that invoked it.

All in all a strange behavior, so I wanted to report this.