I'm having strange issues after my first CM4.2 to UCM6.1 upgrade, every time I try to list on screen more than 100 ip phones using the new UCM6.1 web interface, I get some blanks on the last 15 or 20 phones displayed, so I have to be more specific or reduce the search to 50 or less items. I'm using the last IE.
Other strange issue is for example if a new extension has the number 2345 I continue to see it unregistered although I just finish to refresh and click the find button again and again, but if change the screen filter to show all the extensions beginning with "234" after that I get the 2345 registered. So I think these issues are a bug?
These issues are almost certainly related to Bugs. Here is one very similar 6.1 example;
CSCsl70392 Bug Details
Status & IP not properly associated on Find & List Phone Page
Under Device > Phone the Status and IP address are not properly associated with the correct devices in the list when multiple devices are listed.
CUCM prior to 126.96.36.1994 performing a phone search that returns multiple results.
View the device status on the Phone page, or narrow the search so only a single phone is displayed.
You should contact Tac for sure.
Hope this helps!