I have exactly the same problem. I also think it’s not a big deal and just some kind of glitch or something, the only way I was able to fix it is to manually rename the duplicated text layer.
The source text is different, but the layer name and source name on the timeline are the same as the original layer that I duplicated.
It is odd, but as long as the source text is different, I think it’s just copying some information from the original layer