Jason - I could be wrong but I believe their official stance was that if you wanted to get optimum performance out of their previous Sun Forte panels, then they recommend that the +ve branch of the DC string is earthed. For this reason they dictated that you should NOT use a TL inverter when choosing to do that. However, apparently their new (not sure if available yet) modules do not need to be +ve grounded and, therefore, the use of TL inverters is not prohibited.
That's my take on it anyway, I'm sure others who are sourcing/using these BenQ modules will clarify.