MATE terminal does not become transparent

I used to like to make the terminal semi-transparent, but recently this doesn't work on Trisqeul 9.
When I change the transparency, the colour changes to match the transparency, but it doesn't become transparent.
About a month or two ago this started to happen after reinstalling Trisqeul, but sometimes it became transparent. Now it doesn't become at all.
Does anyone have any ideas?