I was just filling in a certain space with the /fill command when I messed up big time - I wanted to hollow the area (just the edges) but entered replace AND masked. Why - I do not know.
Anyway, after discovering a small space inside had been destroyed by my mistake, I went ahead and made another mistake by deleting the replace and leaving masked where it was, which is just as bad since it is not a [dataValue] option, but the error message I received was:

There is no such item with the ID minecraft:masked

No no, I entered minecraft:stone 6, I'm sure of it:

There is no such item with the ID minecraft:masked

This is clearly a glitch at work, and to prove it, the screenshot shows the error, along with the command I have been entering.