after cleaning registry with ccleaner view of calc.exe brokes like this:
(can't attach PNG picture)
After restoring registry backup *.reg files problem remains.
Topic at microsoft support forum (in Russian) http://answers.microsoft.com/ru-ru/windows/forum/windows8_1-system/%D0%BA%D1%80%D0%B8%D0%B2%D0%BE/ae4549f6-2b7e-4b55-a3f0-b7c1f6c16641
Not sure what has caused this but it seems to have been happening for a while on Windows, it may have something to do with localisation.
You can look at these threads that may help (use at your own risk):
https://social.technet.microsoft.com/Forums/windows/en-US/87cfe0bf-ee80-44d7-85a7-bc618cc12033/halfdigit-in-windows-calculator?forum=w7itproui the last 2 posts seem to have fixed the issue.
http://www.sevenforums.com/general-discussion/56318-half-digits-problem-calculator-2.html the last post has a fix that you can try if you want
first solution works well
thank you!
Glad I could help.