I recently used the website built-in editor to change a file directly. My summary was:
“Added Sucuri.net as a decent CloudFlare alternative & added Impurva Incapsula as a not-so-good CF alternative.”
That’s ~110 chars. I got the error “Commit summary must contain at most 100 characters.” So I shortened the summary, but the “commit” button remained insensitive so there’s no way to submit. When I did a control-r, the original summary is restored, so the error repeats. The only way out of this cycle is to abandon the change and start over.