Copy Paste Broken across workflows

### Custom Node Testing

- [x] I have tried disabling custom nodes and the issue persists (see [how to disable custom nodes](https://docs.comfy.org/troubleshooting/custom-node-issues#step-1%3A-test-with-all-custom-nodes-disabled) if you need help)

### Expected Behavior

When I press Ctrl-C on one workflow then Ctrl-V on another workflow, I expect it to paste the nodes, just like it does on one workflow.

### Actual Behavior

Ctrl-C then Ctrl-V on one workflow works.
Ctrl-C then Ctrl-V on another workflow doesn't work.

### Steps to Reproduce

Select some nodes. Press Ctrl-C.
Change to another workflow.
Ctrl-V, nothing happens.

### Debug Logs

```powershell
Checkpoint files will always be loaded safely.
Total VRAM 24230 MB, total RAM 64192 MB
pytorch version: 2.7.0+cu128
Set vram state to: NORMAL_VRAM
Device: cuda:0 NVIDIA GeForce RTX 3090 : cudaMallocAsync
Using pytorch attention
Python version: 3.12.3 (main, Feb 4 2025, 14:48:35) [GCC 13.3.0]
ComfyUI version: 0.3.40
ComfyUI frontend version: 1.21.7
```

### Other

_No response_