I have the same kind of issue, using Mac OS X with the latest Google Chrome and WordPress 3.9.1 with the Nimble Portfolio Premium plugin.
When sorting items by category, some of them just disapeared...
You can check the web page here : http://blog.esl-france.com/actualites/applications-smartphone/
I'm sorry to post my problem here but I couldn't post it on the Support : You do not have sufficient permissions to access this page
Many thanks for your help