macOS 27.2.2 + Photoshop 2027: Brush picker suddenly opens while painting with Apple Pencil via Sidecar, then clicks are ignored (keyboard still works)

Environment:
- Mac mini M2 Pro, macOS 27.2.2
- Photoshop 2027
- iPad Pro 11-inch (4th gen) used as a Sidecar display, with Apple Pencil
- Trackpad as the Mac's pointing device

Steps to reproduce:
1. Place a Photoshop document window on the Sidecar iPad display.
2. Select the Brush tool and paint (e.g., filling areas) with Apple Pencil.
3. After a while, the brush preset picker (Diameter / Hardness / brush list) opens by itself.

Actual result:
After the picker opens, Photoshop accepts keyboard input only. The cursor still moves, but clicks from both the trackpad and Apple Pencil are ignored. Photoshop is not frozen: I can save (Cmd+S) and quit (Cmd+Q) with the keyboard.

Expected result:
The brush picker should not open unless I request it, and clicks should keep working.

What I tried (no effect):
Esc, Cmd+Tab to another app and back, physical trackpad click and two-finger click, tapping the iPad with Apple Pencil and finger, disconnecting and reconnecting Sidecar.

Workaround:
Save with Cmd+S, quit with Cmd+Q, and relaunch Photoshop.

Notes:
The problem started after updating to macOS 27. The brush cursor also often reverts to an arrow. I only paint on the iPad, so I have not tested whether it happens on the main display.