That is a bug - I've reported 2 tickets back in March regarding issues with the channel-plan pop-up.
One was fixed in 10.01.04.0011 and the second one in 10.01.05.0008.
So you'd need to upgrade to the latest release.
From the release notes....
wns0014416 & wns0014415, Fixed channel plan pop-up when adjusting large number of APs in multi-edit
Here a screenshot of the issue...