Try the transition with the same letters but in a different order, or with different words altogether. For example: "ABCD EFGHI" on the first slide and then "IHGFE DCBA" on the second. Then you will see what it does.
If you use different words from one slide to the other, it will rearrange the letters that are used on both slide and then fade out the letters not needed and fade in other letter that are needed. For example try "Testing" on the first slide and "Guide" on the second. Since there are no "T,s,t,n" in Guide, those letters fade out, but the "e", "g" and "i" are moved.
Not saying that it is a great transition, but it does have a does have some uses.