I realized that vte doesn't implement the repeat character escape sequence while writing a basic ncurses program. Ncurses will intelligently emit this sequence if 7 or more of the same characters are printed to the screen, but only if terminfo reports that this escape sequence is supported. Notably, if the $TERM environment variable is set to "xterm" or "xterm-256color" for example, then it is claimed to be supported and ncurses will emit this repeat character escape sequence.

But because vte doesn't implement it, characters get lost when using any terminal that is based on it, such as gnome-terminal or xfce4-terminal, with many of the common $TERM settings.

To reproduce:

$ export $TERM=xterm
$ echo -e "a\x1B[10b"

The expected result is that the letter 'a' is printed 10 times.
Instead the letter 'a' is only printed once.
The expected result is output correctly when using xterm or UXTerm.