Typing font in a cell

I cannot understand the following problem.
Whenever I type text in a cell the typing font changes to Calibri.
When I hit enter the font changes to the font defined for that cell (fe Arial 10).
It doesn't matter whether I type in the cell or in the text window above the spreadsheet.
When I go to a cell with text (in Arial 10) and I enter text, the text will be in Calibri 10 until I leave the cell.

Why is the typing font different?
But only the typing font, the moment the typing is finished and I leave the cell the font is correct.
Size of the typing font will follow the size defined for that cell.

I tried changing the default font to Arial but still same problem.

interesting. this could possibly be corruption? little chance of course, but it IS possible. office products aren't the best in the world, although Microsoft is starting to care a little more I think. Some of the people I worked for a few months ago saw their Outlook programs go down due to an MS server update. what a surprise, right? well, 6 hours later it was back up. so not bad for a global company! maybe they had nothing else to do? (j/k) have you tried the following?

=> right click each cell individually and go to "cell properties" and set the font in that menu?
=> double clicking the cell first, then start typing the text?
=> NOT double clicking the cell first, and just start typing with actually not causing the cursor to blink when injecting itself into the cell?
=> changing each cell individually through the interface font type OPTION? E.G. - the dropdown list in your image?
=> deleting the offending worksheet completely and trying the same process on an UNUSED worksheet?
=> starting a brand new workbook file and trying the process in it?

do any of those work?

Tried the following:
- try excel sheet on a different computer -> no problem
- try with excel sheet received by email from somebody else -> problem

=> right click each cell individually and go to "cell properties" and set the font in that menu?
Right clicking shows the correct font and size; made the font and size jump up and down and clicked ok
-> still same problem

=> double clicking the cell first, then start typing the text?
That's what I usually do to enter text (as mentioned earlier field above the sheet also gives problem)
-> still same problem

=> NOT double clicking the cell first, and just start typing with actually not causing the cursor to blink when injecting itself into the cell?
-> still same problem

=> deleting the offending worksheet completely and trying the same process on an UNUSED worksheet?
-> same problem with ALL worksheets (new ones or existing ones)