Changing distribution parameter does not change anything when group by is applied

When group by is applied distribution parameters seem not to do anything. What I understand it only controls curve representing theoretical distribution which disappears when group_by is applied.
```r
devtools::load_all("~/nest/teal/")
devtools::load_all("~/nest/teal.devel/")
devtools::load_all("~/nest/teal.modules.general/")
library(scda)
ADSL <- synthetic_cdisc_data("latest")$adsl
#'
vars1 <- choices_selected(variable_choices(ADSL, c("ARM", "COUNTRY", "SEX")), selected = NULL)
#'
app <- init(
data = cdisc_data(
cdisc_dataset("ADSL", ADSL),
code = "ADSL <- synthetic_cdisc_data(\"latest\")$adsl",
check = FALSE
),
modules = root_modules(
tm_g_distribution(
dist_var = data_extract_spec(
dataname = "ADSL",
select = select_spec(
choices = variable_choices(ADSL, c("AGE", "BMRKR1")),
selected = "BMRKR1",
multiple = FALSE,
fixed = FALSE
)
),
strata_var = data_extract_spec(
dataname = "ADSL",
filter = filter_spec(
vars = vars1,
multiple = TRUE
)
),
group_var = data_extract_spec(
dataname = "ADSL",
filter = filter_spec(
vars = vars1,
multiple = TRUE
)
)
)
)
)
shinyApp(app$ui, app$server)

```

Start by running the supplied reproducible Shiny app with tm_g_distribution and compare the distribution parameters with and without group_by applied. Inspect the tm_g_distribution grouping and plot behavior to determine why the theoretical curve disappears or ignores parameter changes. Done means changing distribution parameters produces the expected visible effect when group_by is used.

Written by the indexing model from the issue text.