I'm not sure why InDesign behaves that way, but it's not good technique anyway to use blank spaces to adjust alignment. It's better to use tabs or indents for precise control.

I've found tabs in right-aligned text to be a little tricky (probably because I just don't do that very often), so I'd probably use use a "right indent" to shift that line over. That setting can be accessed in the control panel at the top of your window. However it will adjust the entire paragraph that you've selected, so you'd need to make a hard return above and below that line (rather than the soft returns you have now) so that InDesign views that line as a separate paragraph.

Thanks for the good tip, JamesM.