That seems like a problem with Vim, then… Typically I don’t align at all, so I’m not familiar with editor behavior for alignment; I prefer to just indent one level deeper.

That’s not how you should mix tabs and spaces for alignment. You use the same number of tabs as the previous line, and then fill the remaining width with spaces. That way, when you change tab width, the alignment spaces will always start in the same column as the line they’re aligning to, regardless of the tab width.