Thanks so much for your response, Otto. It is helpful to eliminate possible sources of this formatting issue.
I noticed the formatting changed immediately after I installed Tumblr Importer, so the change must have been a result of how I installed the plug in. I’ll keep working on restoring the formatting.
If you happen to have any hunches of places I might look to undo this change let me know (you look like a wordpress pro, which is why I mention it).
Thanks again!