...try deleting the preferences file for illustator odd behaviour:
If manually deleting this file, ensure Illustrator is closed first.
With Illustrator CS and later, it is also possible to delete the preferences by holding down CTRL+ALT+SHIFT(Win)/Shift+Option+Command(Mac) whilst starting the application and responding 'Yes' when prompted.
Illustrator preferences are stored in the file Aiprefs. This file has no file extension, is a hidden file, and its location is dependent upon the operating system version.
Windows:
To locate the file from Windows Explorer it is necessary to set Explorer Folder options > View to "View Hidden Files and Folders"
Under Win XP and Win 2K, the file will be located in:
%systemdrive%\Documents and Settings\~username\Application Data\Adobe\Adobe Illustrator[Version][Settings-(CS/CS2)].
Mac OSX:
Users>~username>Library>Preferences>Adobe Illustrator CS Settings>Adobe Illustrator Prefs