Automation transition breaks after delete and undo

### System Information

Manjaro Linux, Intel i7-1255U, 16 GB RAM

### LMMS Version(s)

1.2.2

### Most Recent Working Version

_No response_

### Bug Summary

When I create an automation element (to e. g. create a linear transition for a pan knob of a track) and then delete the element and undo the delete action, the transition looks different than before. It went from a linear transition to a hard transition.
Please take a look at the video that I have attached which shows the behavior.
Also I cannot "undo" this with undo or redo and have to create the transition again.

### Expected Behaviour

The transition of the automation should look the same after the undo action.

### Steps To Reproduce

1. Open LMMS with an empty project
2. Create an automation element in the automation track
3. Drag a variable element (e. g. the Pan knob of the Triple Oscillator) to the automation element
4. Create a linear transition (e. g. from left to right in case of Pan)
5. Close the automation editor
6. Delete the automation element by pushing the scroll wheel down
7. Undo using Ctrl+Z

### Logs

A peculiar line that appears when dragging something to the automation element

  QPixmap::grabWidget is deprecated, use QWidget::grab() instead

### Screenshots / Minimum Reproducible Project

https://github.com/user-attachments/assets/7938a802-5389-463e-8225-bd2f8ea7056b

### Please search the issue tracker for existing bug reports before submitting your own.

- [x] I have searched all existing issues and confirmed that this is not a duplicate.

Start in LMMS's automation editor by reproducing the delete-and-undo sequence from the issue and tracing how the automation element and its transition are restored. Done means a linear transition remains linear after deleting the automation element and undoing with Ctrl+Z, without needing to recreate it.

Written by the indexing model from the issue text.