Consider the following wikitext:
;<b>foo:bar</b>:bat
In PHP, this will result in:
<dl><dt><b>foo:bar</b></dt><dd>bat</dd></dl>
However, in Parsoid we don't generate the <dd> for bat -- the final colon is treated literally, not as the start of the definition.
See https://gerrit.wikimedia.org/r/#/c/192615/ and https://github.com/wikimedia/parsoid/blob/master/lib/wt2html/tt/ListHandler.js#L29-L30 which are probably related.
Well, this works fine,
;<b>foo bar</b>:bat
The problem is that in,
;foo:bar:bat
the second colon is rightly ignored.
But in the test case,
;<b>foo:bar</b>:bat
what happens is the first colon gets tokenized as a tag and, similarly, the second is ignored.
Then, in the listHanlder's onListItem, the numOpenTags suppresses the dd in the tag, returning just the colon string instead, resulting in no dd's on the line. However, at that point it's too late restore the ignored second colon to a tag, short of retokenizing to the end of the line.
Something else that works fine now is,
;<b class="fo:o">bar</b>:bat
Fixing this is going to be tricky. It's likely the same fix as in T99843 and looks like I started on a patch in https://gerrit.wikimedia.org/r/#/c/194587 but abandoned it for the time being.