Mint-Y-Dark control theme: LibreOffice Writer icons seem badly wrong

[ghost]

Using the above theme, on Mint 18.3 Cinnamon, produces a kind of low-contrast, flat effect that is surely not what is intended, even though that effect - that theming of Writer - is enabled automatically when Mint's 'use a dark theme where possible' option is enabled.

Screenshot:

Libre Office 5.1.6.2

If this is the wrong place to report this problem, then I apologise; please direct me to the right place.

EDIT: Also, here is Libre Office's 'about' window.

And here are my theme settings (which I provide for information, not because anything is wrong with the window in which they - those settings - appear):