References can resolve to an implicit heading ID in a different document

[glaebhoerl]

(v1.3.20)

Description

If in first.md I have:

# Introduction

and in second.md I have

# Introduction
...
# Section
Link to [introduction][#introduction]

then that link takes me to the Introduction in first.md, rather than the one in second.md! (I suspect in general it's "whichever document comes first in the ToC".)

Proposed solution

Implicit heading references should only resolve within the same document.

Additional notes

I notice there's an MEP that seems to specify the same thing:

Implicit references are not available project wide, and are only accessible in the current document, as many documents follow similar structures (Abstract, Introduction, Methods, Summary).

[rowanc1]

This is surprising and feels like a regression. It was absolutely designed the way you describe.