is it normal for my oscar to leap for freedom out of the tank when i open the lid

Your Oscar is not jumping to get out of the tank, it is probably to do with feeding. In the wild, Oscars feed mainly on insects that fall into the water. Try and imagine an Oscar under a low hanging branch, there may be something that's very close to the water, I'm quite sure an Oscar will lurch out of the water to get it. They will probably also jump out of the water to grab things that are hovering just above the surface, that's why people often get bitten when they are holding the food just above. This is probably why the Oscars have a habit of jumping, unfortunately out of the tank occasionally

Reminds me of arowanas.

I think OFL is right on this one. The jumping is why cover glass and/or tank lids are a must when it comes to keeping oscars

I know a few folks that have come home to their Oscars on the floor. They don't have a solid reputation as escapees but they certainly are powerful enough to try it. When my Oscars get spooked they sometimes dart whichever direction seems safest. Sometimes that direction is Up. Just like delboybully said, make sure you've got a good lid. As far as your situation alixxbongo, yours are probably just happy to see you.