Copying one setting from a settings category now causes all settings within that category which were not copied to reset to default value upon pasting

Copying one setting from a settings category now causes all settings within that category which were not copied to reset to default value upon pasting.  For instance, if I have a handful of images with various configurations set under “Light”, and I choose to copy only the “Contrast” setting from that category and paste it to the other images, it will copy the contrast setting successfully but zero out all other settings under the “Light” category.  This is new behavior, as I have been able to copy and paste contrast additively without it resetting all the other sliders under “Light” up until now.

Also, the behaviour is inconsistent - sometimes it does what I want (pastes contrast setting and leaves the rest of the settings under “Light” alone), and sometimes it wipes all other settings and only retains the updated contrast setting.

Lightroom version: 9.5.1 x64 [ 20260815-1945-84a45bf ] (Aug 15 2026)
NGL Version: 1.43.0.5
WF Version: 8.5 20b9f90
VF Version: 1.0.164
HIL Version: 40501
CAI Version: adobe_api/1.66.1
PH Version: 6.1.1
Adobe GSDK Version: 1.4.0.213
CR Version: 29.0.0.202506270808_710830c
Catalog ID: abf0117f44a64ab5a7ac54f25d080f20

Operating system: Windows 11
OS Version: Windows 11 Pro (2009)
Application architecture: x64
System architecture: x64
Computer model: ASUS System Product Name / AMD Ryzen 7 7800X3D 8-Core Processor           
Logical processor count: 16
Processor speed: 4.2 GHz
Real memory available to Lightroom: 31913.2 MB
Real memory used by Lightroom: 7232.3 MB (22.6%)
Virtual memory used by Lightroom: 15660.3 MB
Memory cache size: 6857.3 MB

Internal Camera Raw version: 18.5.1 [ 2685 ]
Maximum thread count used by Camera Raw: 9
Camera Raw SIMD optimization: SSE2,AVX,AVX2
Camera Raw virtual memory: 1277MB / 13908MB (9%)
Camera Raw real memory: 1289MB / 31913MB (4%)

Display: 3840x1600
System DPI setting: 96 DPI
Dark Mode: Yes
Desktop composition enabled: Yes
Input types: Multitouch: No, Integrated touch: No, Integrated pen: No, External touch: No, External pen: No, Keyboard: No

Graphics Processor Info: DirectX: NVIDIA GeForce RTX 3080 (32.0.16.1088) - 10 GB
Graphics Processor Detail: loaded: Yes, supported: Yes, compute: Yes, init: I4_GPU4, hard: success, soft: success, al: Yes, dl: No
OS Media Capability: true

Application Folder: C:\Program Files\Adobe\Adobe Lightroom CC
Settings Folder: C:\Users\jimmy\AppData\Roaming\Adobe\Lightroom CC
Library Folder: C:\Users\jimmy\AppData\Local\Adobe\Lightroom CC\Data