I’ve linked to observations here from my blog. I had been using the truncated form of the link - i.e. with the observation number, but without the text on the end. WordPress had been rendering these as struckthrough. I investigated this morning, and found that WordPress was classifying these as broken links (even though they work); with that understanding I’ve discovered by adding the text at the end of the link WordPress treats them as working links.
My guess is that the server returns a different status when it performs a redirect than for a direct link to a page, and WordPress treats that as indication of a broken link. I don’t know whether to point the finger at iSpot, at WordPress, or at myself, but I’m mentioning the issue so that people know that it exists.