Inconsistent UWP DateTimeFormatter output for similar patterns with en-US culture

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Assessment

Difficulty
5/5
Estimated time
Over a week
Newbie friendliness
35/100
Issue type
Bug
Clarity
Needs clarification
Activity status
Quiet
Tech stack
csharp
Domain
internationalization

Research direction

Start with the DateTimeFormatter reproduction in the issue using the two en-US patterns and compare their outputs. The payload names no repository file or test; done would require determining whether the inconsistent ordering is an actionable sample issue or platform behavior and documenting the result.

Written by the indexing model from the issue text.

Description

bug

I'm using Windows.Globalization.DateTimeFormatting.DateTimeFormatter in a UWP app with the culture set to "en-US". I noticed inconsistent formatting between two similar patterns.

Scenario:
Pattern: "day month.abbreviated year hour minute"
→ Output: 03-Jun-25 10:53 AM

Pattern: "day month.abbreviated hour minute"
→ Output: Jun 3 10:53 AM

Despite both using "day" and "month.abbreviated", the order of components differs depending on whether year is included or not.

Expectation:
Both formats should follow a consistent order like MM/dd/yyyy for a given culture ("en-US" in this case).

Ways to Reproduce:

string format1 = "day month.abbreviated year hour minute";
string format2 = "day month.abbreviated hour minute"
DateTimeFormatter formatter1 = new DateTimeFormatter(format1 , new[] { "en-US" });
DateTimeFormatter formatter2 = new DateTimeFormatter(format2 , new[] { "en-US" });
var output1 = formatter1.Format(DateTime.Now);
var output2 = formatter2.Format(DateTime.Now);
Dominant language
JavaScript
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