If I recall correctly there is a patch for navigation issues on a multi-row block which we encountered during the upgrade at a place I worked previously. I'm not sure of the bug number but you should be able to find it on MOS.
In the interim though I'd recommend using CTRL+Down to create a new record instead of tabbing through all the fields. In fact personally I do that anyway - I never use the mouse for such navigation purposes.
But the same issue does not replicate in my PC for example... I can navigate to a new row or column using the mouse so maybe a patch is not necessary?
Sounds like the "sticky mouse" or forms focus issue. Not sure if you are on R12 or 11i, but please review the following docs:
Useful Articles for the Oracle E-Business Suite Technology Stack for Technical Consultant / DBA (Doc ID 828157.1)
Diagnosing Forms Mouse Focus Problems Using JRE (Doc ID 760250.1)
Deploying JRE (Native Plug-in) for Windows Clients in Oracle E-Business Suite Release 12 (Doc ID 393931.1)
Upgrading OracleAS 10g Forms and Reports in Oracle E-Business Suite Release 12 [ID 437878.1]
Upgrading to the OracleAS 10g 10.1.3.4 Patch Set in Oracle E-Business Suite Release 12 [ID 728531.1]
I am on EBS R12.1 and thank you for the links.
If the same user does not have the issue when logging in using your PC, then likely it is an issue with the users PC - possibly browser add-ins or toolbars ?