As of Programmer's Notepad 2.2, double-clicking to select text with the PHP scheme selected includes the $ dollar character, e.g. all of $variable will be selected. This behaviour was requested specifically by many PHP users.
To change this behaviour open up WebFiles.scheme and find the wordchars attribute in the PHP language, e.g.
Remove the $ from the attribute. Also do the same for phpscript.scheme if you use that.