I had a MK 2 Zephyr back in 1982, that had a Humber Hark 4 speed up behind a modified Zephyr six.
The turd would jump out of top gear, so I made a little shorty occy strap that went from the seat adjuster.
You'd pull 4th and slip the strap over the shifter and it was fine.
One day on a downshift, I forgot to unhook the strap first, shoved the lever into third like it was a race car
That pulled the strap tight until it released the seat adjuster, just as I took my hand off the shifter, it slammed back into 4th.
By then, as I recall, the clutch was back out, so we ended up getting the odd sharp edge off the 4th gear syncho.
The seat took off one way, somebody took off the other way.... It might have been me.
Never ever, did again though.