Wrong calendar calculations

As is well known, the first week of 1900’s date system is:
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1 = Sun; 2 = Mon; 3 = Tue; 4 = Wed; 5 = Thu; 6 = Fri; 7 = Sat.
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With this in mind, let’s create two copies of the drop-down list to select the day of the week as a certain parameter of the model. One list will be in the form of numbers (actually the days of the week), and the second one will be formatted with the date format mask: ‘ddd’. Look at the picture. Try look for Saturday in the formated drop-down list:
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See, in the formatted list of the week days Saturday (day 7th) is missing! But there are two Mondays! Not bad, isn’t it? Ask your customers: do they like this functionality?
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The funny thing is that Subx has known about this error since autumn 2015:
https://quantrix.com/answers/questions/question/whether-qm-correctly-calculates-dates/
Almost 4 years had expired. There is no saying, how many still years does it take Subx to fix calendar calculations.
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Any feedbacks are welcomed.