It appears that discussions marked as "Solved" does not display attachments that have been attached to replies that have been added to the discussion after the discussion has been marked as "Solved".
Here's a discussion that has (had?) attachments to the original question (and perhaps a reply).
I rember seeing the attachment earlier. Now that it's been marked with an Accepted Solution the attachment links aren't shown.
We could be attributing it to the "Accepted Solution" action incorrectly. It is possible that you made some changes to the layout at the same time and that's what's causing it.
Looks like this is an issue from my custom attachments component -- it's using the parent's attachments for the child's, if any attachments exist on the parent node, i.e., the initial question.
I'll be able to fix this as soon as Lithium completes their current review of the site and allows us to work on components again. My apologies for the inconvenience, and thanks for pointing this out!