@Zulokin
I'm not calling you dumb, no. If I came about that way, I apologize, it was not my intention.

However, many posts here go on ranting about bugs, with added sceenshots, where one can clearly see the reason things did not work out as the player intended. While stating that they looked at everthing and did not miss anything. It is easy to miss an effect or ability, when it almost never has any game relevance.

There have also been posts, with sceenshots, where things are clearly bugged. Combat is fundamental to the game, and Arena handles it very well. A bug in something this basic is simply less likely than the player missing something, in my experience. And without a screenshot or log file there is nothing to go of of to even attempt to fix the bug, if there is one.

@Apersundae
The attacker in the case here has trample and was blocked only by a single creature. With nothing else involved, the attacker kills the blocker in the first strike combat damage step, and gets to trample over the now nonexisting blocker in the second combat damage step.

Double strike, like first strike, creates a second combat damage step, and like first strike governs which creatures get to deal combat damage during the two combat damage steps. No card can overwrite this.

Once blocked an attacker stays blocked until it is removed from combat or the combat phase ends, whichever comes first. If the attacker has nothing left to assign combat damage to, it assigns no combat damage. Trample allows the attacker to assign combat damage to the player/planeswalker/battle it attacked, if all blockers have been assigned lethal damage. If no blocker remains to assign damage to, all combat damage must be assigned to that player/planeswalker/battle. After combat damage has been assigned all of it is dealt as a single event. Trample only ever applies in the combat damage step's turn based action of assigning combat damage, it simply changes how combat damage can be assigned. There is no before or after. There is no targeting involved in blocking or assigning/dealing combat damage.

Combat ends after the end of combat step, which comes after the combat damage step. Arena usually skips that step, but you can set a stop to that point in Arena while in the combat phase.

I believe I've seen this before, and figured that, correct me if I'm wrong, double strike only applies during combat phase, unless a card overrides that. Once something absorbs the first strike and dies, the attacking creature can't target anything different because combat is over and it can't switch targets to something else, even with trample because trample would have to go through the blocker at the blocking phase, and original blocker is dead.

If you could change targets after blockers were declared that might open up trampling in to other creatures, so trample only applies when more damage is delt to the blocker(s) once combat is over, and it goes to it's owner, and combat is over when the blocker(s) is/are dead.

I haven't played paper Magic, so if that's not how that should work they do need to look at the coding.

no there were no other effects this was a bug i was hoping could get some attention,
seems like your just calling me dumb or blind buddy i wouldn't take the time to make this post i promise you. its a bug.

With only those things involved, yes. However, since that is seemingly not what transpired, there were most likely other effects involved, like damage prevention, or the defender also having first strike/double strike, for example.