Using cumin r2779, if not connected to a broker the console hangs when clicking on the Grid tab. Hang: browser indicates it is waiting, Firefox status bar "waiting for ..." along with a "processing" mouse icon. cumin process is also using 75% of CPU.
This actually happens even when connected to a broker with Grid data.
I've not been able to reproduce this with newer versions of cumin. You might consider closing this bug.
Unable to reproduce with cumin r2901. Tried with and without broker connected.