MultiplexerTransform sometimes not enough

[frnhr]

I find that sometimes I get the Duplicate callback outputs error with MultiplexerTransform enabled.

Did some digging, but not sure what's happening. I'll try to do some more digging when I catch the time.

Here is what I know:

• I'm using clientside callbacks a lot, and I have seen this only for a few clientside callbacks
• Debugging inside the MultiplexerTransform.apply, the "problematic" callbacks are in fact found and the allow_duplicate flag is set as you would expect.
• Yet still, I get the Duplicate callback outputs in the UI
• Adding allow_duplicate=True on the callbacks resolves the issue.
• This only happens for some callbacks, other duplicate-output callbacks (clientside and serverside alike) work just fine, i.e. no need to set the flag.

[emilhe]

Would you be able to provide a MWE that demonstrates the bug? 🙃