Two date columns as characters, rbind changes only one to serial no

Question

I have two dataframes that I am using rbind on. Both have a column which is a date in character format. When it rbinds, it changes one of the date characters to serial no format rather than keeping the formatting it had.

all.changed <- rbind(all.changes, changed)
class(all.changes$Updated)
class(changed$Updated)
class(all.changed$Updated)

> class(all.changes$Updated)
[1] "character"
> class(changed$Updated)
[1] "character"
> class(all.changed$Updated)
[1] "character"

As shown above, I've verified that both are class character. Not sure what else to do.