Problem: With the advent of Mac OS X 10.4, the default "text double-click selection" behavior was changed so that when double-clicking a key in an AppleScript record, not only the key would be selected, but in certain cases, also its value along with it.
For example, double-clicking aKey in the following line in Script Editor will select the entire aKey:aValue string:
{aKey:aValue, anotherKey:"itsStringValue"}
Workaround: In the International System Preferences pane, under the Language tab, set the Word Break pop-up value from Standard to English (United States, Computer). End of problem.
Mac OS X Hints
http://hints.macworld.com/article.php?story=2006050817551646