Though I do not consider it as a bug, but would be a good feature to have.
In the mean time, you may try following workaround to achieve same result.
I suggest, you create one more function - Function C and set the dependencies in PS1 as Function A -> Function B and Function B -> Function C
Also, in the last stage of decomposition of FunctionC (ie SignificantUpdate) set a condition, so that FunctionC Executable component will be created for DELETE line.
Similarly, in the last stage of decomposition of FunctionA (ie SignificantUpdate) set a condition, so that FunctionA Executable component will be created for ADD line.
Obviously, you have to take necessary care to ensure, both of the executable components (A, C) send payload to same target system.