Problem with section field, inherited permissions and file uploads

Can't edit and save nodes after adding files if the node belong to a Subspace that relies on inherited permissions. The section field value disappear while saving the node.

Criteria / steps to reproduce:

- Create a subspace that inherit the users and permissions from the parent space.

- Create a section with a content type that have attached files. We use a custom section and content type but I cannot see any difference with default sections and content types.

- Add or edit some content, add a file to it and try to save.

- Upon saving we get the error "An illegal choice has been detected. Please contact the site administrator." The reason for the error is that the "Section" field is marked red and is blank. For some reason the section disappear during the saving process. It is there (at least visibly) both before and after adding the file.

The only work-around we found is to add our users to the subspace as well as the parent space. Then they can save without problems. Unfortunately this defeats the entire purpose of having inherited permissions.

This only happens when adding files to the node. If just a text field for example is added or changed the node is saved without error. As indicated above this error occur both when adding new content as well as editing existing content.

I can see in the URL that the system try to supply the section using "?oa_section_ref=" with the correct section ID but somewhere in the code it must get lost.