I suggested a few new tag wikis. Most were accepted, but in a few, the tag wiki body was accepted but the corresponding excerpt was rejected, leaving them with no summary.
I inquired about it on Super User meta. It turned out that they had been rejected accidentally by a user who had just gained review privileges (10k repuation). He said,
I thought they were re-writes of previous edits.
More recently, it has happened again, with a different editor (who had also just passed 10000 reputation).
I don't have access to the suggested edit review UI, but it seems that the interface is confusing to users when reviewing suggestions for tag wiki excerpts. Could it be changed to clear up the confusion?
Something similar happened with someone's suggested edit pair with the edit summary "Moved the links from Excerpt to the description.": https://stackoverflow.com/suggested-edits/314646 approved, https://stackoverflow.com/suggested-edits/314797 rejected ("Why did you remove the linky?")