Problem with adding new field to attribute table after performing join by attributes

Question

I am studying ArcMap 10.2 and concentrates on different join operations. I am working on a Personal Geodatabase.

I have digitized some polygons from a raster representing houses and have created a feature class under a certain feature dataset for this purpose. I have further created a table (not within any feature dataset) contains number of people occupy each house. I've used the ID in the polygon layer as a primary key and field named house_number in the table i've formed as a foriegn key.

After joining those two tables - I've received the attached new table:

After that I've tried to add a field (double precision) to use the field calculator, but it caused data to shift from one field to another, messing the attribute table. While in editor mode data is organized as it should be, but after exiting the editor mode it is being shifted back. Photos are attached:

Answer 1

Referring to the comment of @GeoKevin try this:

1. Add field (densitiy) to your polygon feature class (Resid).
2. Join your two tables
3. Use field calculator to calculate the field density. Field calculator will has access to both tables (Resid and Occupied)!

Answer 2

Export the joined table into a new shapefile or feature class, and then add the new field.