I wonder if this is an issue with how validator is displaying the id. As far as I can tell the id is pulled from the markup and isn’t something we’re defining ourselves, for example:
<div id='post_1' itemscope itemtype='http://schema.org/DiscussionForumPosting' class='topic-body crawler-post'>
id='post_1 being the @id
If you click that id section in the validator it correctly highlights the post with the matching id… so it seems the validator can properly identify it.
I notice this behavior on other sites with @id values, for example in the schema data for this stackoverflow.com question:
This has the same issue, https://stackoverflow.com/questions/7227202/answer-38775925 is not actually a valid URL, it suffers from the same error where it should be a # instead of a / https://stackoverflow.com/questions/7227202#answer-38775925.
Are there any indications that this is causing a problem with how this data is used in practice anywhere?