While a tuplet pattern itself is not "technically extra," the notes that make it up are extra until they are defined as tuplets. That may seem like a small difference, but it is one that is helpful to keep in mind when working with computer music notation programs.In your example, Finale did not "know" that you were trying to add the 3rd note of an 8th note triplet. It assumed that you were trying to add a normal 8th note to a measure that was already full. Remember that the program cannot read your mind, so you must let it know that you want tuplets BEFORE you enter them if you don't want to get the "too many beats in the measure" dialog.
As you work with Finale, you will probably see other examples of where the notation you are getting is not what you expected. Usually, it is because you did not set some parameter the way it needs to be set to get what you want. An example would be getting 8th notes to beam in groups of three in 6/8 time. If you set the meter for six 8th notes per bar, Finale will flag each 8th note separately. If you want three 8th notes beamed together in 6/8, you have to set the meter to 2 dotted quarter notes per bar.
Unfortunately, it will probably take a while for you to get used to all of the "oddities" of the program. The online documentation explains most of them, but you have to search a bit to find it. For what it's worth, I started using Finale with version 1.0 and I am still learning shortcuts and tricks after over 10 years of use.
Good luck with your music.
Jim Coull
