onSSR causes injection error when container top-element is identical to content

[neopostmodern]

I have a function that post-processes markdown text to inject images. It will only run correctly on the client, so I use placeholders on the server. This function is called htmlImageIdReplacementHack.

let post = <div dangerouslySetInnerHTML={{__html: htmlImageIdReplacementHack(Marked(content))}}
                style={{marginBottom: '4rem'}}/>;
return <NoSSR key={_id} onSSR={post}>{post}</NoSSR>

This code throws the following warning:

Warning: React attempted to reuse markup in a container but the checksum was invalid. This generally means that you are using server rendering and the markup generated on the server was not what the client was expecting. React injected new markup to compensate which works but you have lost many of the benefits of server rendering. Instead, figure out why the markup being generated is different on the client or server:
 (client) ta-reactid="56"><p><a href="/cfs/files/i
 (server) ta-reactid="56"><p></p><div style="width

If I use onSSR={<i>Loading...</i>} instead everything is fine.

[neopostmodern]

I found the cause of the issue:
Apparently the onSSR block is evaluated on the client too and it only works if the onSSR block yields the same result on the server and on the client. I added a weird flag to my htmlImageIdReplacementHack function and then use Meteor.isServer || simulateSSR in there, but that sounds far from ideal to me.

[lleaff]

To resolve this in a generic way, how about requiring that component props (onSSR), be wrapped in a callback so they aren't evaluated unless it's needed?