Button accelerators not visible (but working)

[UncleOilybag]

I have two laptops - both running Linux Mint 18.2, Xfce 64bit, both with LibreOffice 5.1.6.2 Unless I am completely missing something I have set the LO Tools>Options the same for both computers.

When I set them both up I noticed that in Calc documents with buttons (push buttons or options buttons) the underlined accelerators were not visible. (But they did actually work - I noticed that because I had predetermined the accelerator with the tilde~). This was the same for both laptops

Later I must have altered some setting somewhere (in LO or Linux I know not which!) because now one of my computers shows the accelerators perfectly well but the other doesn’t.

Can anybody tell me where the setting is?

[vsfoote]

UI was changed to hide them, and use to toggle the assigned mnemonic visible.

[UncleOilybag]

L-alt toggle doesn’t seem to do anything.
I think it is something to do with Xcfe settings.

****** STOP PRESS ********
With my various fiddling about with settings I can now see the accelerators on buttons on BOTH laptops.
What did I do?
I’m not 100% sure but I think it was to set Menu>Settings manger > Desktop settings - set dropdown as Xfwm4+compositing THEN DO A RE-BOOT

Hope this helps somebody else if they experience the same problem.