[Orgmode] $LR syntax in tables

[Andrew Stribblehill]

I'm afraid I can't quite wrap my head around this puzzle. I have a little table:

| Budget       |  640 | 640 |
| Some expense | -165 | 475 |
  #+TBLFM: $3=$LR3+$2

So col C is supposed to add the previous line's col C to the current
line's col B.

However, it seems that $LR3 is referring to the _subsequent_ line not
the previous one. Is there a bug or just my misunderstanding?

Thanks.