Tables with blacked-out content

Sometimes cells in a table will be blacked-out. It looks like it's doing some sort of inverted highlighting.

Sometimes the content can be copied and pasted, other times it says the clipboard is empty.

Not sure what the cause is. It's happened with tables imported (Copy into document + import map) from Word. But I've also noticed it with tables made from scratch in FM.

Anyone know what's causing this?