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Summary:
Screen recording here: StatusItemsSlowDownMenusYosemite.mov

When I start an additional application like QuickTime Player's screen recording or xScope, menu tracking across the system slows down to an unusable pace. The mouse arrow stops and jumps. Sometimes there are also similar mouse stoppages when opening *any* new window in any application.

Steps to Reproduce:
1. Start an application that brings up a status item. In the screen recording linked to above I use QuickTime Player's "New Screen Recording" function, but it also works with an arbitrary application like The Icon Factory's xScope out of the Mac App Store.
2. Drag from left to right in the menu bar
3. Single-click a menu to open it

Expected Results:
Mouse tracking should continue like when the application was not running.

Actual Results:
As you see in the screen recording, as long as the additional status item is up. the mouse jumps, menu titles highlight with a large delay, and mouse tracking seems to be otherwise impeded, as a single click should leave the menu open, but it closes immediately after the title has highlighted.

Although the recording doesn't show it, the same effect happens with pop-up menus, like the "methods" popup in Xcode.

Note how quitting QuickTime Player in the screen recording leaves the menu bar slow for a little while longer, but then it normalises. The effect does not occur with applications that do not show a status item, and don't occur in QuickTime Player until the status item is actually shown.

Notes:
This is not related to machine load caused by QuickTime's screen recording itself. As shown, xScope, which doesn't record the screen, isn't doing anything at the time, exhibits the same issue.

Configuration:
Retina iMac 5K Core i7 running in default display mode (@2x)
2. Second 27" screen attached via MiniDisplayPort -> DisplayPort cable (Dell U2711, 2560x1440)
de_at_ulik_dot_at_iMac5K.spx - configuration file has been successfully uploaded.

Attachments:
'de_at_ulik_dot_at_iMac5K.spx' was successfully uploaded.