Captive Network Assistant Woes

I frequently use a wifi network that makes use of a captive portal. Until a few days ago, I had no issue joining the network and logging in through the WebView popup opened by the Captive Network Assistant. Recently, however, the popup has stopped displaying when I connect to the network. I can still open a browser window and land on the captive portal login by trying to surf to any http address, but where did the popup window go?! Curious about the development, I opened up Console and noted the following whenever I joined the network:

2014-05-21 16:22:21.120 UserEventAgent[11]: Captive: [CNInfoNetworkActive:1655] en0: SSID ‘********' making interface primary (cache indicates network not captive)

This is odd, because I know this network uses a captive portal, so for the network to be cached as not captive is buggy.

I did some Googling and found a seemingly related thread that suggested disconnecting from the network, waiting for a session timeout, turning off wireless, and then restarting, in order to clear the Captive Network Assistant cache (https://discussions.apple.com/thread/6079437?answerId=25448430022#25448430022). I followed the outlined procedure, but still no popup. I opened up Console again, and found that while there was no longer a cache message, I was now seeing:

2014-05-21 17:01:03.143 UserEventAgent[11]: Captive: [CNInfoNetworkActive:1655] en0: SSID ‘********' not making interface primary (no cache entry)
2014-05-21 17:01:03.143 UserEventAgent[11]: Captive: CNPluginHandler en0: Evaluating
2014-05-21 17:01:03.143 UserEventAgent[11]: Captive: en0: Probing '********'
2014-05-21 17:01:03.143 UserEventAgent[11]: Captive: [async_http_read_stream:387] kCFStreamEventErrorOccurred NSOSStatusErrorDomain/-9807: The operation couldn’t be completed. (OSStatus error -9807.)
2014-05-21 17:01:03.143 UserEventAgent[11]: Captive: [CaptiveHandleRedirect:1653] Unknown result value: 1, assuming online

So, we see the cache is no longer the issue, but something goes buggy with the probe (i.e., when Captive Network Assistant requests the Apple success webpage), and in its error state it assumes we are online, which we are not. This also seems buggy. What's a little funny, is that as soon as the computer assumes it's online, all my little background processes start making requests, and I get can see a dump of the captive portal login page markup in the errors that those processes throw.

Anyway, I’m probably going to open a bug ticket with Apple about this, but I figured I’d spin up a discussion about it as well just in case anyone has some helpful information.

To be clear, I’m not looking for a way to disable Captive Network Assistant (which is where a lot of the internet discussions on similar issues seem to lead); I like the popup and want it to come back.

System notes: Running a MacBook Pro Retina, Mid 2012, OS X 10.9.3 (13D65); however, this same problem was happening before I upgraded and was running 10.9.2.