custom post field (datamanager class)

[FlyingDutchman]

I have a question regarding the datamanager class.
I'm trying to add a custom field to every post. So I created the custom field in the database. Getting the content out of the database and show up in the post is a piece of cake of course, anyway that just works.

Now I want to be able to let the user fill the custom field with information when replying. So I created a extra field on the newreply page similar to the Title textfield.

I set up a plugin so that the customfield is transported from the $vbulletin->GPC array into the build_new_post() function.

Now it didn't save the custom field value, so i started looking into the function and arrivad at the datamanager classes. An error showed up that my customfield wasn't in $validfields so I thought let's add it to that array (which is in vB_DataManager_Post class)
No errors show up anymore, but still the customfield in the database stays empty.

In vb2 (and vb3 too i think) it was quite easy to add a customfield, just change the newpost query and you're all set, but I kinda get lost in the datamanager class now and obviously I'm overlooking some easy thing I need to do but can anyone please help me out?

thanks for any help, FlyingDutchman