Update button redirects to homepage, without updating

I want to be clear that this is an issue with my computer or my network, but because it only seems to be affecting WordPress, I don’t know where else to go to ask for help.

I currently operate about 30 different WordPress sites for different clients, and it’s the same problem for all of them: when I click the “Update” button after editing a Page, I am redirected to the homepage and all of the edits are lost. This problem does not occur for Posts. I’ve tried on a bunch of sites with different version numbers (up to 4.1). It happens in Firefox, Chrome, and Safari. I am running a Mac with OSX Mavericks.

Does anybody know any network settings that could cause something like this? The problem just popped up overnight, and I don’t recall changing anything major.