Editor crashes when undoing Standard Element creation after New USS is created

Reproduction steps:
1. Create a new project
2. Create any Standard Element (e.g. GameObject > UI Toolkit > Standard Elements > Button)
3. Create UI Document and save changes
4. Create New USS in the Style Sheets window
5. Create any Standard Element (e.g. GameObject > UI Toolkit > Standard Elements > Button)
6. Save changes
7. Undo changes with cmd+z keyboard shortcut and observe the Editor

Actual result: Editor crashes
Expected result: Changes are undone

Reproducible with: 6000.6.0a7, 6000.6.0b3, 6000.7.0a2
Couldn’t reproduce with: 6000.0.79f1, 6000.3.19f1, 6000.5.3f1, 6000.6.0a6 (No Standard Elements option)

Reproduced on: macOS Tahoe 26.5 (M4), Ubuntu 24.04

Notes:

• Issue is not reproducible when undoing changes with context menu
• First few lines of the stack trace:

#0  0x00000186fda5e8 in __pthread_kill
#1  0x00000186f1c644 in abort
#2  0x0000040cb611b8 in monoeg_g_printv
#3  0x0000040cb46748 in mono_log_write_logfile
#4  0x0000040cb613d0 in monoeg_g_logv_nofree