Adding updates to an existing deployment causes clients to get stuck at downloading

Hello all. Sometimes MS will revise or release a patch a few days after Patch Tuesday to address an issue (ex: KB3033395, March 2015). In these cases I simply download the revised update to a package, and then add the update (drag and drop) to the existing deployment. This has worked in the past, but suddenly this week I have ran into the issue a few times.

I can't find any obvious errors in the client log files:

UpdatesDeployment.log: Assignment({19EBE7A1-40A4-451E-B1E0-50BE958482A4}) already in progress state (AssignmentStateDownloading). No need to evaluateUpdatesDeploymentAgent3/17/2015 11:02:38 AM624 (0x0270)
UpdatesHandler.log: Bundle update (f5bcf591-1b57-4904-bbd0-0df0ba9410b0) is requesting download from child updates for action (INSTALL)

CAS.log: Location update from CTM for content 530ff762-1806-4601-aae5-d83d83d89e01.1 and request {4F338AA7-9C94-4064-99A8-6CA9E0B9C3F5}

Download request only, ignoring location updatThe Updates UI is not displayed

The Updates UI is not displayed on the client, the only indication something is wrong is in the log files and reports. 

Any suggestions on where else I could look for the problem?

Thanks!