Wordpress - Post/Page Publish/Update button not clickable once I make an edit

It appears to be a bug, but one that can be hacked around each time it happens with about 2 seconds of work. This wordpress forum thread:

If you're using Chrome, right-click on the greyed-out "Update" button and select "Inspect Element". You will see something to the likes of:

<input name="save" type="submit" class="button button-primary button-large disabled" id="publish" accesskey="p" value="Update">

Just delete the word disabled and the update button will become clickable again. Click it and it should update.

Saved me reloading and losing work.

See also this less resolved thread.

Once I realized it was an issue related to the Page/Post autosave, and not something to do with pasting the data from a text editor, I disabled all plugins to determine if that would be the cause. Disabling the plugins did not seem to have an effect.

No errors were reported in the browser error console.

I manually updated the Wordpress installation and this seems to have fixed the issue. Unfortunatley I do not understand why, none of the files replaced were ever edited by me.