If after reinstalling ZBrush you discover that the cursor does not display its position correctly (for example, if it is shown about 1/4" away from the location where you click) this is either due to the way in which ZBrush was reinstalled or because you are seeing a double header at the top of the ZBrush window.
If the double header is not present, read on:
Even though it is possible to remove a program from the Mac by deleting its folder out of the Applications directory, this is not the preferred way to do so. The best is to run the Uninstall application found in the ZBrush directory. Failing to do so will result in files being left behind elsewhere on your system -- files that may cause conflicts with later installations.
If you are affected by the issue described above, please uninstall ZBrush again. Then go to your system's ~/Library/Saved Application State directory. (An easy way to get there is to be in the Finder and Option+click "Go" at the top of the screen. You'll see "Library" in the pull-down menu. Alternatively, just click Go >> Computer. Now double-click Macintosh HD and you'll see Library as one of the folders there.) Delete any folders found there with "pixologic" in the folder name. Now reinstall ZBrush.
This should resolve the issue.