See https://www.mediawiki.org/w/index.php?title=Topic:Sqiakln6zj2vyqg8&topic_showPostId=sqjazy5nr58n9xdc#flow-post-sqjazy5nr58n9xdc -- the nowiki scenario there can be reproduce on the commandline as follows.
```
[subbu@earth lib] echo "<nowiki> foo" | node parse --dp | sed 's/<script.*<\/script>//g;' | node parse --html2wt
[warning/html2wt][enwiki/Main Page] Parsoid id found on element without a matching data-parsoid entry: ID=mwAg; ELT=<span typeof="mw:Placeholder" id="mwAg"><nowiki></span>
<span><nowiki></span> foo
[subbu@earth lib] echo "<nowiki> foo" | node parse --dp | sed 's/<script.*<\/script>//g;' | node parse --html2wt | node parse --dp | sed 's/<script.*<\/script>//g;' | node parse --html2wt
[warning/html2wt][enwiki/Main Page] Parsoid id found on element without a matching data-parsoid entry: ID=mwAg; ELT=<span typeof="mw:Placeholder" id="mwAg"><nowiki></span>
[warning/html2wt][enwiki/Main Page] Parsoid id found on element without a matching data-parsoid entry: ID=mwAg; ELT=<span id="mwAg"><span typeof="mw:Entity" id="mwAw"><</span>nowiki<span typeof="mw:Entity" id="mwBA">></span></span>
<span><nowiki></span> foo
```
Note how the "<nowiki> foo" changed to "<span><nowiki></span> foo" to "<span><nowiki></span> foo" after 2 roundtrips when data-parsoid is not provided.
Effectively, Parsoid is being asked to serialize Parsoid-HTML but without access to the associated data-parsoid properties.
Is this a RESTBase issue or a Flow issue? Or, is this an expectation that Parsoid should serialize without data-parsoid? If the latter, we should understand this a bit better why.