Reference: <a href="http://www.openoffice.org/issues/show_bug.cgi?id=73696">OpenOffice issue 73696</a>
Adobe Reader refuses to save a PDF form after the user has entered information into it. According to the corresponding OpenOffice report, this is due to Adobe's used of undocumented features.
The OpenOffice issue was closed for the bizarre reason that this feature "is probably undocumented intentionally". Of course it is! This allows Adobe to maintain a monopoly on a very important feature of PDF forms, namely, the ability to actually save them.
One hopes that the LibreOffice developers will take a more active interest in researching and implementing this feature!
I doubt that that will be "fixed" by LibO. It's Adobe's intention that only very special forms can be saved with inserted data by AR. It seems that for creation of those forms a special software will have to be purchased. I know that some German authorities tested that for several time. I filled and saved some forms for "Deutsche Rentenversicherung", but it seems they decided to stop using that.
Of course Our developers can try to outfox Adobe, but that might be illegal, and they have to work on more important issues.
You can simply use Foxit Reader, afaik it still (I did not test for several weeks) can save filled forms created with OOo PDF export.