This is a bug in the plugs firmware. Apparently, a read of a certain attribute makes things go wrong there. I do not recall which one it was as this was already enough for me personally to run away from Tuya as fast as I could.
The above is the response the device sends, note the non-existent endpoint. When deconz receives that response, it things that particular endpoint has been forgotten and adds it. A DDF for that device would not prevent the endpoint popping up in the GUI, but it would prevent creating of an additional light.
Regarding the name change, when deconz joing new devices, the REST API plugin has a function to translate the original Tuya naming (manufacturer and model ID) to a more meaningful vendor/product for known devices. When reading the basic cluster and therefore the respective attributes via GUI, that function is NOT executed. Hence, the true values are picked up and displayed. The translation approach seemed to be a promising way at the beginning, but has proven to be too challenging to maintain due to the naming chaos accros Tuya and their respecive vendors.