Question: Bug in plottools[transform] & Where is transform/object

On Maple 16.02, plattools[transform] only works for very simple procedures. It does not work for procedures with the `if` function even with the simple arrow definition. or with any if-block in a more general proc definition.

With the sequence of commands:

simp:=plot(sin(x), x=0..Pi);
f:=(xx,yy)->`if`(yy > 0, [xx,4*yy], [xx,yy]);
trns:=plottools:-transform(f);
trns(simp);

The first three statements run without error messages. At the last statement I get the error message: 

Error, (in trns) ambiguous multiple assignment

From examining op(trns), the error seems to occur in the procedure: `transform/object`. However, I cannot find a way to print out this procedure, even with verboseproc=2, with print or op. Where is this procedure, and how can I print it out?

On the other hand, with f:=(xx,yy)-> [xx, 3*max(0,yy)+yy], the transform works and produces the same plot as the non-working sequence above. Unfortunately, I cannot find the same kind of trick for the plot and function I really need to use.