When moving an entire tree of pages to another space, using the 'with children' checkbox on the page Edit tab, links which use a different case than the corresponding page names which they link to have the old space's name prefixed to them, and are therefore broken (since the pages have been moved to the new space and no longer exist in the old space).

For a while I wasn't sure which pages had this problem, but now I definitely can say there is a clear and definite pattern: only those links which use a different case than the linked-to page names are affected.