The solid behaviour has nothing to do with physics. It's to be twinned together with the 'platform' behaviour.
What you want to do for those things that you gave the solid behaviour to is give them the physics behaviour and then set the 'immovable' trait to yes. This means that it's solid and won't move. Other sprites (that are not immovable of course!) will then be able to interact with it as if it were/solid/a platform/an obstacle etc.
It's not advisable to have physics and platform behaviours in the same layout really - it leads to some unpredicatable and screwy behaviour. Decide which one is going to be better for your project (physics/platform) and then run with that.
Let me know if that answers your question.