A new update is available for the Advanced Custom Fields plugin! This update contains fixes for some pesky bugs, adds support for the new tinymce version in WP 3.9 and adds new logic to help speed up saving data.
Core: Improved efficiency and speed when saving values by removing ACF meta from the native WP postmeta box
Field Group: Fixed cache issue causing field settings to not update
WYSIWYG field: Added support for new tinymce 4 in WP 3.9
Number field: Fixed bug causing blank values to save as 0
Google Maps field: Fixed JS bug causing google maps to not render when Google library is already loaded
Validation: Fixed JS bug where hidden field groups’s fields were being validated