We have tested the latest version of OSX, released this week, 10.7.2.
In Capture One 6.3.1 this update appears to have broken the brush tool used for spot/dust correction and local adjustment layers. These tools remain useable but the cursor no longer changes to an outline of the brush, and instead remains a standard cursor.
For this reason we’d recommend most Capture One users not to update to 10.7.2 until there is an update to Capture One to address this.
Update: this also applies to other cursors like the white balance cursor (thanks Paul for reporting this).