Design is not consistent when swapping figures that have fixed aspect ratio.

[ltuijnder]

While working on a solution for issue: #271 I stumbled upon the following bug:

Say I have 3 figures with aspect ratio 1 and I want two of them to be nicely placed below a the third:
I can get the desired result using the following code:

library(ggplot2)
library(patchwork)
p1 <- ggplot(mtcars) + geom_point(aes(mpg, disp)) + theme(aspect.ratio = 1)

design <- "
  33
  12
    "
p1 + p1 + p1 + plot_layout(design = design, height = unit(c(2,-1),c("null","null")))

^{Created on 2021-08-26 by the reprex package (v2.0.1)}

However, when I just permutate the numbers in design I get another result:

library(ggplot2)
library(patchwork)
p1 <- ggplot(mtcars) + geom_point(aes(mpg, disp)) + theme(aspect.ratio = 1)
design <- "
  11
  23
    "
p1 + p1 + p1 + plot_layout(design = design, height = unit(c(2,-1),c("null","null")))

^{Created on 2021-08-26 by the reprex package (v2.0.1)}

I would have expected the exact same figure as the layout specification is the same and the 3 subplots are identical.

---

Note that this issue does not seem to occur when the figure up top does not have an aspect ratio specified.