Here is the solution.
///////////////////////////////////////////////////////////////////////////////////////////////////////
// Disable the original line of code responsible for clearing the text field after media file uploaded
///////////////////////////////////////////////////////////////////////////////////////////////////////
Buddykit.js
FilesAdded: function(up, files) {
$('#buddykit-filelist-wrap').show();
// Filter maximum number of downloads.
if ( buddyKitFiles.length >= __buddyKit.config.options.buddykit_field_max_image_number ) {
alert('You have reached the allowed number of images per post.');
} else {
plupload.each( files,
function(file) {
document.getElementById(__buddyKit.file_list_container_id ).innerHTML += '<li id="'+file.id+'" class="buddykit-filelist-item">' + ' (' + plupload.formatSize(file.size) + ') <b></b></div>';
});
////////////////////////////////////////////////////////////////////
// It is not neccesary to clear text area after media file uploaded.
// Therefore I've disabled the line of code below.
// $('#whats-new').focus().val('').selectRange(0,0);
////////////////////////////////////////////////////////////////////
uploader.start();
}
},