A former Microsoft engineer has described a late-stage Word 97 bug that repeatedly crashed in testing but disappeared whenever developers used a debugger, making it exceptionally difficult to investigate. The issue mattered because an intermittent lab fault risked becoming a frequent real-world problem after release, potentially undermining one of Microsoft’s major Office launches.

The team eventually linked the crash to a CPU erratum affecting one manufacturer’s processors. Although a newer compiler avoided the faulty instruction sequence, Microsoft’s tools were already locked down, so engineers instead searched the finished binaries and inserted a single NOP (“no operation”) instruction as a targeted patch; this quiet fix helped stabilise Word 97 alongside more visible additions such as Clippy and VBA.