Context: Mac - Yosemite - LC 6.7.5 Commercial or LC 6.7.6 Community Edition.
1) Open the Activity monitor
2) open LC from the Dock.
3) Select Menu File->Open stack
4) Go for a coffee... for almost 30 seconds!
During this time, can't interact with anything else.
Even the activity monitor is fully blocked
5) Have back the control, the activity monitor screen is updated,
and here a screenshot of the past OS activity (blue) 6) Re-selecting File->Open stack a second time, it works fine.
7) Closing LC and repeating this process, it stucks again.

Any clue or already known bug about this?
Thanks
Thierry