The PHP parser (for enwiki config) parses:
```
[[mw:Flow#What happens to my custom signature?]]
```
as:
```
<a href="//www.mediawiki.org/wiki/Flow#What_happens_to_my_custom_signature.3F" class="extiw" title="mw:Flow">mw:Flow#What happens to my custom signature?</a>
```
See https://en.wikipedia.org/w/index.php?title=User:Mattflaschen_(WMF)/Sandbox&oldid=654710957
Parsoid (verified using [form](http://parsoid-lb.eqiad.wikimedia.org/_wikitext/) which also uses enwiki config) parses it as:
```
<a rel="mw:ExtLink" href="//www.mediawiki.org/wiki/Flow#What happens to my custom signature?" title="mw:Flow" data-parsoid="{"stx":"simple","a":{"href":"//www.mediawiki.org/wiki/Flow#What happens to my custom signature?"},"sa":{"href":"mw:Flow#What happens to my custom signature?"},"isIW":true,"dsr":[0,48,2,2]}">mw:Flow#What happens to my custom signature?</a>
```
The [interwiki table](https://www.mediawiki.org/wiki/Manual:Interwiki_table) has an `iw_local` local field which I suspect is involved here (since the section encoding is just the standard encoding you would get if it were not an interwiki link).
Original report below:
---
The anchor of this link is not generated correctly:
https://pt.wikipedia.org/w/index.php?title=T%C3%B3pico:Segov5w2cbzfrzck&topic_showPostId=seq389fse5fxehcx#flow-post-seq389fse5fxehcx
It points to
https://www.mediawiki.org/wiki/Flow#What%20happens%20to%20my%20custom%20signature?
but it should point to
https://www.mediawiki.org/wiki/Flow#What_happens_to_my_custom_signature.3F