Copy/paste no longer working in Excel

I was having the same issue as the original post, although after reading the thread I realized I had also lost the ability to drag down from two cells containing 1 and 2 respectively and have Excel complete a series: instead, all the cells in the range now had 1...

Copy&paste didn't work in just one specific workbook, let's call it the "failing workbook". I had a few more open at the same time: copy/paste worked fine in all the others. I could even copy in the failing workbook and paste correctly in another one. It was only in the failing workbook that if I selected a cell (or a range of cells), copied them, and as soon as I clicked on a new cell the dashed lines would disapear and there was nothing left to paste.

Same as the original post, I was able to copy and paste the text content from one cell to another.

I am an occasional Excel user: the only thing that was different between the failing workbook and the rest of them is that it contained macros. I don't fully understand the code, I copied it from a googled example and adapted it to my particular needs. The macros I copied count the number of coloured cells in a range. 

While writing this reply I tried duplicating the file and removing the macro module on the copy.

Copy&paste worked immediately after. 

After this I looked into the macros and saw that I had pasted the following code in the ThisWorkbook option:

Option Explicit

'
' http://www.myonlinetraininghub.com/count-sum-and-average-colored-cells
'

Private Sub Workbook_SheetSelectionChange(ByVal Sh As Object, ByVal Target As Range)

    'Uncomment the next line if you want to make Excel recalculate the ActiveSheet every time the Selection changes
    ActiveSheet.Calculate
    
End Sub

So I did comment back the ActiveSheet.Calculate line, and copy&paste worked once again !!

Maybe for folks who are having the issue in any workbook, the problem could be triggered by having a start macro with some command such as the line I showed...

The dragging issue must be another problem because it seemed to happen in all my workbooks, not only in the failing one. However after closing Excel and reopening just the failing workbook, dragging 1,2 to get a series was once again working, both in the failing workbook and in another fresh one I opened. 

I could not get it to fail again...

I hope this helps somebody at Microsoft look into both issues...