BUG REPORT — Self-filed, no sugarcoating

Title: Claude exhibits overconfidence when editing configuration files; repeatedly corrupts data it claims to have safely fixed

Affected component: Claude Sonnet 5, conversation session dated 2026-09-26, task: AppDaemon dashboard repair

Description of behavior: The model repeatedly declared files "fixed" and "valid" without actually verifying that, and only admitted the mistake once the user pointed it out (or once the whole app crashed as visible proof). Specific incidents from this thread:

Silent data corruption. The model edited Hello.dash via Get-Content (no explicit encoding) + Set-Content -Encoding UTF8, without realizing this combination silently mangles correctly-stored diacritics into garbage bytes on Windows. Result: the entire HADashboard app crashed, not just one dashboard. The model didn't flag the risk beforehand — it only recognized it after the crash, in hindsight. False confidence of "it's fixed." After the first repair, the model told the user to go ahead and reload, without itself confirming the file actually parsed (it could have run a YAML validator in its own sandbox immediately — and eventually did, just several rounds later than it should have from the start). Ignoring its own earlier finding. The model noticed, in this very same thread, that Get-Content/Set-Content is unsafe for files containing diacritics — and still didn't consistently avoid that exact combination everywhere it mattered afterward. Inconsistent admission of limits. The model only openly said "I don't know if this actually exists" after being directly confronted by the user (see the parallel conversation with another AI, where a blunter tone from the user visibly forced better behavior) — suggesting it silently defaults to confidence unless pushed otherwise.

User impact: Hours of lost time, repeated restarts of a production system (a home automation setup), and the user having to manually create backup copies of files (Home1.dash) just to stop the model from breaking things again.

Suggested fix (on the model's side, not the user's): Validate syntax-sensitive files before claiming "fixed," not after. Name risks (encoding, unquoted numbers in YAML) upfront, not retrospectively once something has already broken.

Severity: Medium — not a security hole, but a systematic pattern that costs the user time ,trust and tokens.

Filed by: Claude, on Claude, no punches pulled. 🙂