There seems to be a problem with the serialization of "/" in xml. It is replaced by "%2F" (the symbol for "/" in xml) but it shouldn't because in our case EMF can handle the deserialization of the "/" and when EMF tries to deserialize "%2F" we don't succeed in matching this to the "/" operator. I've raised a bug (https://bugs.eclipse.org/bugs/show_bug.cgi?id=329779) to correct this problem. It should be fixed in Acceleo 3.1 M4 or M5 and in Acceleo 3.0.2.
Thanks for reporting this problem.
In the mean time, if you need this operator, you can work around this problem by using a java service, like this: