Welcome to the forum and thank you for your questions. The 2 star and 3 star alignment process allows the user to select any star in the alignment star list and then selects the 2nd and 3rd star as needed based on the position of the first star. I will need to test this behavior to see what the issue might be here. Also, if anyone would care to test Rick's specific scenario to verify repeatability that would be great.
What might be going on is that after selecting the first star the ExploreStars alignment routine pares down the list to only those stars that meet certain criteria for distance from the second star, and also how close it is to the horizon. This may be what is restricting you from selecting the second star you want to use. The list is pared down further in terms of the 3rd star if you are doing a 3 star alignment.
I will test this to verify that is what is going on, or if there is something else wrong.
Director Electrical Engineering
Explore Scientific, LLC.