Union operation destroys the part and removes negate effect

Bug Reports Studio Bugs
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1

Hello, im experiencing a strange issue with Union Operation on Roblox Studio.

The issue:
When I try to create a Union using a negated part, the operations fails. Instead of creating a Union the orginal part disappears, and the negated part loses its negation and becomes a normal part

Steps to reproduce::

  1. Create two new Parts.
  2. Place one Part inside the other.
  3. Negate the inner Part.
  4. Select both parts and Union.
    **Expected behavior: **
    A Union should be created, with the negated Part cutting a hole in the other Part.

Actual behavior:
The original Part disappears, while the negated Part simply becomes a normal Part. No UnionOperation is created. Also there is a error/information in output “[CSG] AllowNegatePrimaryPart: primary is negated, using alternate property source”

I’ve attached a video demonstrating the issue:

2026-07-09 23-08-58|video

The launcher of Roblox Studio is the newest.

Zrzut ekranu 2026-07-09 231539|316x205

Device Specifications:

  • Device: Acer Nitro 5
  • Operating System: Windows 11 (64-bit)
  • CPU: Intel Core i5-11400H (11th Gen, 2.70 GHz)
  • GPU: NVIDIA GeForce RTX 3050 Laptop GPU
  • RAM: 16 GB
  • Architecture: x64
3 Likes
2

Thanks for reporting this. I have a hunch what might be causing this. While I look into a fix, I think you can do either to workaround this bug

  1. negate the negative part twice
  2. select the non-negative part first
1 Like
3
  1. Negating the part twice does not do anything; the issue remains.
  2. Selecting the non-negative part first worked, but after the UnionOperation, the Negate object turned in to Part and remained where it was instead of being destroyed.
4

I am actually having trouble reproducing the issue. Are you able to share an rbxm with the two parts ? Also can you let me know if you have the ‘Solid Modeling on Meshes’ and/or ‘Improved Studio Solid Modeling Controls’ enabled?

5

I’m using parts from explorer (next to terrain option) but sure I can sent parts via RBXM.

Parts.rbxm (7.9 KB)

1 Like
6

I didnt see the next sentence. Sorry,. Where can i enable/disable those options?

EDIT: I turned on Improved Studio Solid Modeling Controls and restaring now studio, I cant see the Solid Modeling on Meshes option.

1 Like
7

If you go to File->Beta Features you should see both of those options.

8

Ohh, I turned the Studio Solid Modeling Controls and it works now. Idk who thought that hiding and disabling this option was a good idea. Thank you for help.

1 Like
9

Very odd, cannot reproduce with your parts either :thinking:

10

Ah glad that made it work for you. We are actually planning to remove that beta soon so that should force everyone to use the code path that doesn’t have this bug.
One last thing, can you let me know if you had ‘Solid Modeling on Meshes’ turned on before turning on the ‘Improved Studio Controls’ fixed it?

1 Like
11

Solid Modeling on Meshes was turned off default. Just by turning on Improved Studio Controls the UnionOperations were fixed.

1 Like
12

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