Can't edit post date with UI nor database / PHPMyAdmin

I can’t edit the publishing date of my post. When I do this via the UI, in the right bar of the editing page, it would reset the original date back, even after doing all the necessary (changing the date, clicking “OK” and “Save”).

I decided to change it directly in the database: same result. I changed the date in the wp_posts table, where I altered the date in the columns post_date and post_date_gmt (<- correctly), even in post_modified and post_modified_gmt as well.

When I go back to the editing page, I see the right post date is given. But when I hit edit, just to check out, and fill out the proper date, and save it, it would put back the original date once again? Where does he get that date from? I thought I modified it all? There must be a little spot in the database where this original post date (or timestamp) is still lingering around.

I need to get this figured out because a plug-in (TouchCarousel) is using the post date to order the items. It would keep dat very post in front while it should be somewhere more in the middle. I disabled this plugin to check if it wasn’t actually causing this – it didn’t.

I’m not sure if it’s of any importance, but it’s a multilingual website.

Can someone help me out please?