Mouse focus / respponse to mouse and keyboard input

Hi, We have a very large Forms 6i application. We are testing now to replace Jinitiator with Sun Plug-In / JRE 1.6.0_20 due to the rollout of Windows7 64 bit clients. On some forms the mouse focus is lost or it does not respond to mouse clicks, but generally does to tab input . Also, when a form opens the cursor goes into the correct start field for a split second and then jumps elsewhere like the to the menu canvas or is just lost unit you click into a field. We have a project in work that will upgrade Forms 10g,