I completely agree that in the situation shown by the teaser the dress is almost a minor detail (as it could be, sadly, in RL).
For me the "dress issue" came up immediately during the first play through because it seemed an odd choice, without even knowing what could happen next. It's the kind of (cute) dress that you can wear on a date or e.g. for hanging out with a girlfriend (well, I let you have the final word on that

) not to meet your molester. And not just because it could inspire some possible threat of violence in him. It's just does not sound right, at least IMO.
Now, just to be extremely clear, for me it's not a major issue that will ruin the game and so on. It's an interesting topic of discussion while we wait but at the same time I don't want it blowing out of proportion in the discussions.
It's a choice he made, whether it is good or bad is up to discussion but it's still in the realm of speculations until we will see what actually happen (and maybe have the "issue" addressed somehow in the dialogues).
So it's with this spirit that I'd try to bring up this *possible* interpretation that in part I already mentioned but I found a little support in the dialogues in the hallway before the 4th task.
When she decides to remove the bra in front of them she says:
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I wouldn't say that she is now "comfortable" around Aiden to not even care about being naked in front of him, but somehow the vibe that the whole sequence give is that she has somehow accepted the "game" and the perverted requests that he might ask her. While she obviously still hate him and his manners, the rules of the game have been set and established, so she kinda know what to expect:
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And sure, since each new task is a step up, she is still surprised and disgusted by the requests, but she knows very well the nature of them.
So this could at least in part explain the dress, she "does not care" anymore, she knows that there will be some weird requests to satisfy and willingly or subconsciously she "does not care" about the dress she is wearing for the meeting. I put the "does not care" in quotes as I don't mean it literally as she would bare herself in front of him in a snap of a finger.
Put it in lame terms the reasoning will be something along the lines "well he already saw me naked and groped me, it's not that this dress will be worst than that" (I'm obviously over-simplifying).
I know that is not a perfect explanation, even because it does not catch all the nuances of the different paths with which she is going to have the meeting (4th task fulfilled or not, Morello or not, what happened before in the 3rd task etc). But at least it could be coherent with the corruption and the established dynamic between the two characters.
This is a possible interpretation. I still think that there will be another "mirror moment" like before Sam's concert and before going to school for the 4th task in which the choice of the dress will be somehow addressed.
No it's not a bug in the code, Morello can happen if the task is fulfilled, if she chooses to stop or if she didn't exposed the breast during the 3rd task there is not even the possibility of accepting the task.
And your scenario is very possible IMO, I almost suspect that the initial choice to get the hell out of there could be even tied to Morello's choice: for example the choice could be only possible if she asked Morello's help as in that case she can leaving knowing that she has already a solution (which also brings in the question why going if you have a solution, but I diverge). Or it could be the other way around, if you asked Morello's help she'll leave without a choice. Something like that.