The safeguard filter is comically unintelligent. One of my side projects is a strategy game, and in that strategy game one player has a set of jokes, one of them referring to "biological minds". Whenever Fable reads this asset it immediately stops - because of the use of word 'biological', there is nothing else biological about that codebase.

And there is a bug to this bug, if the downgrade happens at close to full context window, there is no taking over this session with Opus -- happened to me twice: it throws some context window exceeded error, suggesting what fits in Fable context, may not fit in Opus's around the maximum. And then and there, an entire session is lost. In fact, there are two bugs, as /resuming such broken session attempts to resume with Fable, burning through tokens.

Oh well, I learned to be careful with the jokes around Fable.