`vjust` is ignored in `position_stack()` in 4.0.0

[SCasanova]

I found a problem when updating the package to 4.0.0 in one of my visualizations. In a column chart, the labels produced by geom_text() used position = position_stack(vjust = 0.5) to center in the middle of the bars. The argument is now getting ignored.

Here is the code to reproduce the bug:

``` r
library(ggplot2)


test <- tibble::tibble(bin = seq(3), count = c(23,22,10))

ggplot(test, aes(x = bin, y = count))+
  geom_col(position = 'dodge',
           width=0.99,
           fill = '#DC9542',
           alpha = 0.85)+
  theme_minimal()+
  geom_text(
    aes(label = round(count, 2), y = count + 1),
    position = position_stack(vjust = 0)
  )

ggplot(test, aes(x = bin, y = count))+
  geom_col(position = 'dodge',
           width=0.99,
           fill = '#DC9542',
           alpha = 0.85)+
  theme_minimal()+
  geom_text(
    aes(label = round(count, 2), y = count + 1),
    position = position_stack(vjust = 1)
  )

ggplot(test, aes(x = bin, y = count))+
  geom_col(position = 'dodge',
           width=0.99,
           fill = '#DC9542',
           alpha = 0.85)+
  theme_minimal()+
  geom_text(
    aes(label = round(count, 2), y = count + 1),
    position = position_stack(vjust = 0.5)
  )

^{Created on 2025-10-09 with reprex v2.1.1}

[sambtalcott]

I discovered this same bug today. Interestingly it works fine if there are multiple groups, but not if there is a single group:

library(ggplot2)

q <- tibble::tribble(
  ~group, ~f,   ~p,
  "A",    "f1", .5,
  "A",    "f2", .5,
  "B",    "f1", 1
)
q |> 
  ggplot(aes(group, p, fill = f)) + 
  geom_col(position = "stack") + 
  geom_text(aes(label = p), position = position_stack(vjust = 0.5))

q2 <-tibble::tribble(
  ~group, ~f,   ~p,
  "A",    "f1", 1,
  "B",    "f1", 1
)

q2 |> 
  ggplot(aes(group, p, fill = f)) + 
  geom_col(position = "stack") + 
  geom_text(aes(label = p), position = position_stack(vjust = 0.5))

^{Created on 2025-10-09 with reprex v2.1.1}

[teunbrand]

Thanks for the reports, I can confirm this on my end as well.