`dplyr::case_when`: `TRUE ~` not same as the `.default = ` for variable outside data

[ynsec37]

library(dplyr)
#> Warning: package 'dplyr' was built under R version 4.5.1
#> 
#> Attaching package: 'dplyr'
#> The following objects are masked from 'package:stats':
#> 
#>     filter, lag
#> The following objects are masked from 'package:base':
#> 
#>     intersect, setdiff, setequal, union
packageVersion('dplyr')
#> [1] '1.1.4'
df <- tibble::tibble(a = c(1, 2))
x <- TRUE # variable outside the data 
df |>
  mutate(
    a = case_when(
      .env$x ~ 1,
      TRUE ~ a
    )
  )
#> # A tibble: 2 × 1
#>       a
#>   <dbl>
#> 1     1
#> 2     1

df |>
  mutate(
    a = case_when(
      .env$x ~ 1,
      .default = a
    )
  )
#> Error in `mutate()`:
#> ℹ In argument: `a = case_when(.env$x ~ 1, .default = a)`.
#> Caused by error in `case_when()`:
#> ! `.default` must have size 1, not size 2.