[plt-scheme] call/ec tail calls

The documentation for call/ec states that "the application of call/ec's 
argument is not a tail call," which seems odd given that R5RS states the 
application of call/cc's argument must be a tail call.  However in all the 
test cases that I've been able to come up with that should grow without bound, 
were the application of call/ec's argument not a tail call, I've found they 
don't grow at all.  So is this a documentation bug (call/ec really does apply 
it's argument as a tail call), or am I just not able to find such an example 
that grows without bound using call/ec (could someone provide such an 
example)?  If the documentation is correct, why can't call/ec do the tail call 
while call/cc can?

Thanks in advance.

-d