The gemara says that there is a machlokes r' nachman and r' sheishes whether the violation of "stealing and selling" applies only when the sale is actually binding, or is one chayev to pay 4 and 5 even when the sale is not actually binding (such as prior to yi'ush). R' Nachman holds that even if the sale isn't actually binding one is chayev just for the action of attempting to sell. R' Sheishes holds that one is only chayev if the sale is actually binding, just as tevicha is actually binding.
The rashash discusses how this fits with the discussion in temurah about כל מידי דעביד רחמנא לא תעביד, אי עביד לא מהני - where abaya and rava argue whether by the torah placing an issur, it is preventing the action from being binding. For example, the torah says that one cannot divorce after motzi shem ra - they argue whether the divorce will be effective. The rashash suggests that in our gemara all would agree with rava that אי עביד לא מהני and one can be punished just for the action, even though it is not binding. His rationale seems to be that according to r' nachman you are getting malkus just for going through the motions of selling, even though it is not binding. Even R' sheishes only disagrees that the sale must be binding because we learn it from tevicha, but in concept he will agree that one can get malkus for the action. This seems to be like rava who says that one can get malkus even though it isn't binding, not like abaya who says that one can get NOT get malkus unless the act is effective.
The Chavos Da'as (y.d. 1:11) holds that the rationale of rava that אי עביד לא מהני is that in order to avoid the violation the torah prevents the action from being chal. Meaning, only when there is a violation that must be avoided, does the torah prevent the "chalos" of the issur. Basically, it is a tool that the torah creates to prevent a situation that it doesn't want. This would really only apply to a situation where there is a l'av for the violation, not just a penalty for doing an action. In short, according to the chavos da'as (and i believe r' akiva eiger says the same) that rava's concept only applies to a case where there is a violation, it is not applicable over here. Therefore, we must say that the requirement to sell an object that still belongs to the original owner is a direct contradiction to the concept of the sale being binding. This paradox forces r' nachman to say that you are chayev for the action of trying to sell, even though it isn't binding. Based on this, our gemara can work out both according to abaya and rava in temura because it has not connection at all.