Odd insistence on ungroup()

dplyr weirdness.R

library(dplyr)
library(tidyr)
myDF <- data.frame(A = sample(LETTERS[1:4], 100, replace = TRUE),
                   B = sample(letters[5:9], 100, replace = TRUE),
                   C = rnorm(100))
summaryDF <- myDF %>% group_by(A, B) %>% dplyr::summarise(meanC = mean(C))
summaryDF %>% spread(B, meanC)  # Error: index out of bounds
summaryDF %>% ungroup() %>% spread(B, meanC)  # Works

The above code actually does work now (at least for me) I find some dplyr nuisances are actually caused by the data being a Tibble. Maybe that was the problem 4 years ago...