ReplacementTransform not working properly with add function

## Description of bug / unexpected behavior

The first text does not disappear and after the and it suddenly disappears and doubled.

## Expected behavior

We expected that the first text disapear and replaced by the second text. When move the square the second text move as well.

## How to reproduce the issue

Code for reproducing the problem

```py
square=Square(side_length=1)

tex=Tex("$\\sqrt{2}+1$")

tex2=Tex("$\\frac{x}{\\sqrt{2}}$")

square.add(tex)

self.play(Write(square))

self.play(ReplacementTransform(tex,tex2),run_time=2)

self.play(ApplyMethod(square.shift,UP*2))
```

## Additional media files

Images/GIFs


Start by running the provided reproduction using Square.add, ReplacementTransform, and ApplyMethod to observe when the first text disappears and whether the replacement moves with the square. Trace those named animation operations and verify that the first text is replaced once and the second text remains attached when the square shifts.

Written by the indexing model from the issue text.