WORK AROUND
While we wait for Microsoft to discover this bug and release a fix, here's one crude work around for setting the Field Size of a new Number Field:
Select: File->Options->Object Designers
In the Table design view section use the Default number Field Size ComboBox to select one of the following:
Byte, Integer, Long Integer, Sing, Double, Decimal, Replication ID
Then click "OK" to save your options
When you return to the Table designer and create a new Number field it will now default to your selected Field Size.
Every time you wish to change Number Field Sizes you will need to return to Options and re-select the appropriate default Field Size.
This workaround will not allow you to change the Field Size for existing number fields.
It is also possible to use SQL DDL to create a new table using commands.