This happens only on my new MacBook Air 11" and only since I upgraded to Mountain Lion.
Whenever my mouse pointer is over a Numbers document (not the window title, but the actual document), CPU usage by Numbers.app goes to 70% and stays there until I move my mouse somewhere else.
Did anyone else experience this?
I get a small burst of Numbers activity when I move the cursor over a table in Numbers, and another burst when I move the cursor back off the table. Haven't seen it go even as high as 10% on this mid-2010 MBP. So, no problem here. I have about 850 MB of free RAM and about 175 GB of free HD. If I find myself in a situation where the free RAM is about gone, I'll try this again and see what difference that makes.
Just as an illustration. This is activity monitor in background sorted by CPU descending, and Numbers.app in the foreground. The mouse pointer sits over Number's big gray window title bar.
Now just the same, but moved the mouse pointer downwards onto the document content:
And it's really always 70% on my machine. Never 100% or 50% or anything else. Always between 69% and 71%.
I let my free RAM drop below 800 MB and my Numbers CPU load rose to 70% when hovering mouse over table. I closed unneeded apps and Restarted computer, resulting in over 2 GB Free RAM. Numbers CPU load was less than 5% at all times when mousing over table, same Numbers document in both cases.
I have 8 GB memory on my computer and CPU usage is still about 70%.
I also tried the following things:
1) Restarted the computer
2) Reinstalled Numbers with the latest version from the App Store
3) Verified Numbers file permissions
4) Checked that I don't have any corrupted fonts on my computer
5) Ran opensnoop to see if Numbers has any weird disk activity during the high CPU usage
Still no luck.
By the way, I sent some days ago a bug report to Apple concerning this issue by using the Numbers/Provide Numbers Feedback menu. This sends you to a web page where you can choose feedback type "bug report".
I recommend that you do it too if you have not done it yet.
You guys are doing the right thing in reporting this. I'm not trying to convince you of anything one way or the other, just reporting what is going on in my case. On my side, I'll be upgrading to 8GB.
I'll continue to look for clues as to the cause.
Edit: Please, if you haven't, test with only Numbers and Activity Monitor running.
I tested to run Numbers without having any other applications running. Before that I deleted the following preferences / cache files and let Numbers to re-create them.
I also tried to run it with another user account (admin) in case there is something wrong with my user profile.
In both cases Numbers CPU usage is still high.