I too had stop button problems. I think it happens if you have used the earlier version and upgraded. The cure is to quit Ethernal and find the preferences file
edu.usfca.jean.bovet.Ethernal.plist from
~/Library/Preferences/
and maybe the "Ethernal" Folder in "~/Library/Application Support/"

After deleting those and relaunch it works for me.

Sometimes the Search function misreports some simple searches on captured packets (for example 'xy') in that a packet is found displayed that does not in fact contain the string xy but deleting that search phrase then typing it in again finds no packets with that string.

Something useful to have would be to have a way to additionally resolve some addresses to my own local table of host names or colours which can be loaded on future captures, maybe displayed as a separate column.

However this is Application shows lots of promise. Keep up the good work.