In my game (Duck! Me?, yes still flogging that particular dead horse) I have a table (supporter, enterable) on which is a bell jar (container, transparent) which in turn contains a head of celery.
In v4.0, this is shown in the room display as follows and as I’d expect.
You can also see a table (on which is a bell jar (which is closed) (which contains a head of celery)) here.
When I switch to v4.3 (or v4.1 as a test), the display adds a spurious “is”.
You can also see a table (on which is a bell jar (which is closed) (which contains is a head of celery)) here.
If I change the table to be a container (which makes no sense in the game), it reverts to the expected output, without the “is”.
I did compare the source code for this between v4.0 and v4.1 but it seems to have been substantially changed and I couldn’t see an obvious error, although it was getting quite late by then.
Jeremy
N.B. I didn’t try v4.2, I skipped that version.