I edited the description to remove typos. The image didn't appear in the galleries I had selected after I did that. It still appeared in my gallery though.
Hmmm....That's unusual. Most likely what happened is when you initially selected the galleries they didn't save completely. Editing the description goes through a separate process from saving galleries so that shouldn't cause your entry to lose its galleries. give it another try some time and let me know if it still happens.