Hello Taylor.
This issue is similar to another instrument that I use, an HP 3437A System Voltmeter. It only has 8 commands and generally ignores "generic" HPIB commands like *IDN?, *RST, etc, in this case the instrument just simply returns the measurement being displayed. I love this meter because it is capable of taking 5600 measurements per second. However, my typical sample rate is generally limited to about 350 samples per second due to slower instruments sharing the bus. But just like your HP 3478A these generic HPIB commands are either ignored or cause undesired instrument behavior.
Best Regards,
Craig Petersen.
Craig Petersen