Problems with barcharts with barmode='overlay' and Date objects

I need to plot several barcharts with Date objects on the x-axis with barmode = 'overlay' for a whole year. When there are enough values to plot, everything works fine, as I would like the bars to have equal widths along all traces.

But when one trace has few elements, the width of those traces are expanded.
And when one trace only has 1 value, it is not shown at all.

I could overcome those problems by creating fictional Dates with 0 y-values for the rest of the year, but I was hoping there is a better way of solving that.

The variable n in the example can be used to determine the amount of bars for the problematic
trace.

library(plotly)
n = 3

## All days of 2019 ###############
Days2019 <- data.frame(
  date = seq(as.Date("2019-01-01"), as.Date("2019-12-31"), by = "days")
)

## Sample n Days of 2019 ###############
df <- data.frame(
  date = sort(sample(Days2019$date, size = n, replace = F)),
  val = sample(1:100, n, replace = T)
)

## Merge fictional 0 y-Values #################
# df = merge(df, Days2019, by="date", all=T)
# df[is.na(df$val),]$val=0

## Sample 30 Days of 2019 ###############
holiday1 <- data.frame(
  date = sort(sample(Days2019$date, size = 30, replace = F))
)

## Plot Plotly ###############
maxY = max(df$val)
plot_ly() %>%
  add_trace(data = holiday1, x = ~date, y = maxY, marker = list(color = "gray"), type="bar", name="Holidays") %>% 
  add_trace(data = df, x = ~date, y = ~val, marker = list(color = "red"), type="bar", name="Values") %>% 
  plotly::layout(autosize = F,
                 barmode = 'overlay',
                 bargap = 0.05,
                 xaxis = list(
                   type = "date",
                   range = c(as.Date("2019-01-01")-1,
                             as.Date("2019-12-31")+1),
                   autorange = FALSE,
                   tickmode = "auto",
                   nticks = 14L,
                   automargin = F)
  )

Start by running the supplied R example with n=3, then vary n and compare the bar widths and visibility in overlay mode across the two traces. Trace the plotly.R bar/date handling used by this example and consider the issue done when sparse Date traces retain appropriate widths and a single value is rendered without requiring fictional zero-valued dates.