osv_memory classes seem to share their _columns?

Hi John,

Thanks for providing the test module, it makes your question definitely easier to understand :-)

Your reasoning is correct, but you have overlooked one thing: all osv classes (osv or osv_memory) are supposed to have their own _columns attribute. This is partly due to the internal ORM mechanics for OpenERP inheritance, and partly due to the way Python's own object inheritance works.

To get the correct behavior, make sure to initialize at least an empty _columns dictionary in both wizards. For example add this line right after the declaration of _name or _description:
  _columns = {}

Now on a related note, your wizards seem to do something that is really *not* recommended: altering the _columns of the wizard class itself. This is bad for many reasons, such as interactions by multiple instances, memory leaks, etc.
You may have seen this technique used in other addons, but this should really be avoided.
Instead, consider 2 alternatives:
1) Use "virtual" fields, which are returned in fields_view_get() as if they existed, and handle these virtual fields values properly by overriding read() and write() appropriately, without actually modifying _columns at any time.
2) Instead of creating dynamic fields on the wizard object, have a child osv_memory object displayed in a one2many widget. This way you can have any number of lines and fields (you can even make the o2m list editable, or display it in form view directly, like addresses on partners).

Hope this helps....