Encountering a some odd issues attempting to submit changes on in the CP of an ExpressionEngine 2.7.2 site. Instead of saving the changes and displaying the success message, I'm bounced to a non-existent URL and the landing page of my site is displayed instead.
URL FOR ENTRY:
URL FOR NON-EXISTENT PAGE
Notice how the first URL has double ampersands right before the filter (entry_id=1&&filter=) and the URL of the second domain ends not with an = sign but with %3D.
I've see this error in two separate instances:
1) In a particular textarea field (in a field group which only contains five fields), entering more than 327 characters will trigger the error — even if all of the other fields are empty.
2) Adding new fields to a channel field group, regardless of whether it's a brand-new field group or simply adding a field to an existing group.
Disabling extensions (via the config.php file) is having no impact and the logs are not giving any meaningful data.