OpenIndiana Distribution

This happens to me with MATE-terminal, but not with xterm or the emacs GUI. It only happens occasionally with any application that runs in MATE-terminal, including mutt, the shell, and the pager pg.
Specifically, a character that I type sometimes has no effect on the application. Waiting for a while seems to make no difference. When I type another character, the application responds to both. However, if I move the cursor outside of the MATE-terminal window, the application responds to the missing character. That character seems to be hidden away some place until something like another character or an interrupt sends it up to the application. I don't have a way to reproduce this problem, but it happens frequently enough for me to notice it.
I've learned to work around this problem by moving the cursor outside the window briefly, but it should be fixed. I'm running a version of oi-hipster that was current on 01 July 2018. I'm using the en_US.UTF-8 locale.