Linked controls can cause crashes

[Monospace-V]

System Information

Windows 11

LMMS Version(s)

1.2.0, 1.3.0 alpha from website, 1.3.0-alpha.1.823+8b5297f (unknown platform/unknown processor, Qt 5.15.6, GCC 13-win32).

Most Recent Working Version

No response

Bug Summary

Controls of any kind can be linked via Ctrl-drag: hold down the Ctrl key and drag one controller to another. This links their values to be the same. When one knob is moved, the other one moves too, mirroring its exact value (unlike the Controllers which work based on knob position).
LMMS can be crashed in some cases when using this link ability.

#7488 mentions this issue.
Fixing this issue is important if we want to make the ability to link controls obvious to the user.

Expected Behaviour

No crash when connecting, moving, disconnecting, reconnecting, moving etc the controls.

Steps To Reproduce

You can use two volume knobs for this reproduction, since they are similar. I have used the volume knobs of the 3xOsc and Sample track from the song editor in the default template.

1. Make volume of knob 1 < volume of knob 2
2. Connect 1 to 2 (ctrl and drag volume knob 1 to knob 2)
3. Increase 2
4. Disconnect knobs ("Remove all linked controls")
5. Make volume of knob 1 < volume of knob 2
6. Connect 2 to 1 (ctrl and drag volume knob 2 to knob 1)
7. Increase 2

And here it crashes.

The direction of connection seems to be significant to reproducing this bug. Make note of it.

Logs

No response

Screenshots / Minimum Reproducible Project

Screen.Recording.2025-04-30.232646.mp4

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

• I have searched all existing issues and confirmed that this is not a duplicate.

[bratpeki]

Awesome wallpaper, BTW!

Can recreate very easily.