Curate, connect, and discover
One of the fun things about writing is how, sometimes, you accidentally write things a certain way, and then, weeks later, you realise that what you wrote actually has significance to the story, and it adds a cool little detail to some aspect of the plot or characterisation.
In Fortune's Rule, I've written Starkiller bowing in the presence of his master. Just today, though, I realised that the more proper Sith thing would be to kneel. The true explanation for the bowing instead, of course, is that it was entirely unintentional and in fact carries absolutely no meaning whatsoever. I was a little sloppy and didn't think things through sufficiently.
However, in-world, it looks like some sort of choice on Vader's part. He taught his apprentice to bow (more a Jedi thing, I think?), rather than kneel (a Sith thing, and more subservient). Perhaps Vader's Anakin is showing a little bit, in not wanting to make Starkiller demonstrate the extreme subservience that a Sith master usually expects from their apprentice (i.e. that Sidious expects from him). At the same time, I think it also fits with Vader's character. He's a military leader, not a political one like Sidious, and as such probably prioritizes utility over ceremony. There's no need to bother with the whole kneeling thing, when a bow will do.
I love things like this, because they show how, for all that a lot of planning and intentional symbolism may go into writing, sometimes what the reader sees as significant is just a surprisingly functional mistake. (And it also makes me wonder how much of the stuff we analyzed in high school lit classes was intentional, and how much was coincidental.)