LLM decompiler output that recompiles and passes every shipped test can silently erase a disclosed CVE.

Recompilability and re-executability are the standard metrics, and they reward the wrong behavior: functions that build and pass all shipped tests diverge from the original on a fuzzed corpus 4.9% of the time overall and up to 13% for one system (arXiv 2609.05370). Across 300 real GitHub library functions and 287 CVE-grounded functions, the strongest refinement LLM raised Ghidra's build rate from 75% to 90% while its behavioral match rate fell from 74% to 62%. Up to a tenth of disclosed vulnerabilities showed Crash Absence: the bug vanished from the output with no visible placeholder.