I thought that PHPed was supporting PHP 5.2

Ever since PHP5.1.0, a core function property_exists() has been defined, but PHPed code completion does not recognize this.

I have checked my setup, and I am using PHP5, and I have set file associations for *.php to php5, but still this function is not recognized by PHPed ?

you may want to update list of "predefined funtions and tags" for php5. See tools->settings->reserved words, PHP5 language, Add, Name => property_exists, Returning Value => bool, Argument list => ( mixed $class, string $property )