The `Install-Module` cmdlet in PowerShell does not always respect the `$ErrorActionPreference` variable when it is set to `Stop` from the script scope because `Install-Module` may be designed to use a different preference variable specifically for its error handling, such as `$ProgressPreference`.
In PowerShell, there are different preference variables for controlling different aspects of script behavior. While `$ErrorActionPreference` is used for controlling how non-terminating errors are handled, other cmdlets like `Install-Module` may use `$ProgressPreference` to control the display of progress messages and errors related to installation progress.
If you want to ensure that `Install-Module` behaves according to your error action preference, you should set `$ErrorActionPreference` and `$ProgressPreference` within the same scope where you call the `Install-Module` cmdlet:
```powershell
$ErrorActionPreference = "Stop"
$ProgressPreference = "SilentlyContinue" # Optional, to suppress progress messages
Install-Module -Name ModuleName
```
By setting both preferences within the same scope as the cmdlet, you can have more control over the error handling and progress reporting for that specific operation.