First off, you should use ODAC 11.2 Release 5 or higher. That version is certified with EF 5.
Normally, Number(5) is mapped to an Int16 by default. Not sure how you have it mapped to a Short. In any case, if you want to explicitly map any data type to a non-default data type, you can use the following mapping customization described here in the doc:
The problem was solved, I had to install ODAC 11.2 Release 5 and made a mapping customization in all App.config from mi solution.
Thank you very much for your reply!