The Sims 2 Legacy Collection Self-Modifying Files

Product: The Sims 2: Legacy Collection
Platform: Steam (PC)
Date: March 14, 2025

Summary of the Bug:
When launching or playing The Sims 2: Legacy Collection via Steam, the game modifies three specific game files. Upon verifying the integrity of game files through Steam, it consistently reports "3 files failed to validate and will be reacquired." Using Git, I identified the exact files being modified by the game itself, suggesting that the game is altering its own data during runtime, which conflicts with Steam’s validation process.

Affected Files (Identified via Git):

EP1/TSData/Res/LotTemplates/Dorm_05_Permanent.package

EP6/TSData/Res/LotTemplates/Hotel01_Permanent.package

EP9/TSData/Res/Text/Neighborhood.package

Steps to Reproduce:

Install The Sims 2: Legacy Collection via Steam.
Initialize a Git repository in the game’s installation directory (steam/steamapps/common/The Sims 2 Legacy Collection) to track file changes.
Launch the game and play for a short period (e.g., enter a neighborhood or lot).
Exit the game and check Git status (git status) to confirm the modified files.
In Steam, right-click The Sims 2: Legacy Collection > Properties > Installed Files > "Verify integrity of game files."

Observe Steam’s validation result: "3 files failed to validate and will be reacquired."

Frequency of the Bug:
Every time (100%) – occurs consistently after launching the game and validating files via Steam.

What Happens When the Bug Occurs:

The game modifies the three listed files during gameplay or on launch.
Steam detects these changes during validation and flags them as corrupted or missing, reacquiring them. This cycle repeats each time the game is played and validated, indicating the game itself is altering these files in a way that conflicts with Steam’s expected file integrity.

Expected Behavior:

The game should not modify core files (e.g., .package files in TSData) in a way that causes Steam to flag them as invalid. Steam’s validation should pass without needing to reacquire files after normal gameplay.

Actual Behavior:

The game modifies Dorm_05_Permanent.package, Hotel01_Permanent.package, and Neighborhood.package.
Steam validation fails, reporting "3 files failed to validate," and redownloads these files, only for the issue to recur after the next launch.

Additional Details:

System Specs: Windows 10/11 and Linux with Steam Proton, 

AMD Ryzen 7 3700X, NVIDIA GeForce RTX 3090, 128 GBs, X570 AORUS PRO WIFI

Game Version: Latest version Patch #5 as of February 27 via Steam.

Troubleshooting Attempted:
Reinstalled the game fully via Steam.
Verified file integrity multiple times, consistently showing the same 3 files failing.
Used Git to confirm the game itself is modifying these files, not external factors (e.g., mods or user edits). 

Suspected Cause: The game may be writing runtime data (e.g., neighborhood or lot states) to these .package files, which are intended to be static, causing a mismatch with Steam’s original file hashes.