Column Insert putting contents of opened spreadsheet into other spreadsheet

I have been developing a program over a number of years to number crunch data from spectrometers. I have several open spreadsheets and format them then copy data around, meaningfully. I used "Insert" as below to add columns between previously copied data columns.
Dim insert As Integer
For insert = 4 To 16 Step 2

On doing this, the contents of one of the spreadsheets I have open are pasted in to the new spreadsheets four times. This data seems to be in the paste buffer but I have not copied it in at any point.

This seems to have started happening since the creators update.

I do not need an alternative code solution as I have rewritten this to allow the program to continue working.

Any ideas, anyone?