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CultureAwareComparer with ignore casing serialized on previous versions of .NET Framework does not correctly deserialize on .NET Framework 4.7.1


When deserializing a CultureAwareComparer that was serialized using ignore case on a previous version of .NET Framework on a machine running .NET Framework 4.7.1, the comparer becomes case sensitive.


In the .NET Framework 4.7.1 we added the ability to specify more comparer options when doing a culture-aware comparison. As part of that change we introduced a new field on the comparer that holds the information about what kind of comparison is requested.

When that type, coming from a version of .NET Framework prior to 4.7.1 is deserialized on a .NET Framework 4.7.1 machine, the private field introduced in the .NET Framework 4.7.1 is reset to zero, which makes the comparer case sensitive.


The following 2 comparers are susceptible to this issue. These comparers are usually used with collection types like Dictionary and Hashtable. P:System.StringComparer.InvariantCultureIgnoreCase P:System.StringComparer.CurrentCultureIgnoreCase


Ensure that both serialization and deserialization occurs on systems running a version of the .NET Framework starting with 4.7.1.


If you are running on Windows 10 Fall Creators Update, an update is available that addresses this issue. Select one of the following links based on your processor architecture:



[09-Jan-2018] The fix for this issue is included in the Update for .NET Framework 4.7.1 - KB4054856 for all platforms except Windows 10 Fall Creators Update.