Can't delete a column of data!

I’m using a a rolling 12 month financial calc spreadsheet in LO on Linux Mint 17.3 Mate 64 bit. I’ve renamed the last financial year calc sheet for the current year. As I progress entering current daily data in the calc sheet I delete the next day’s data (last years) column to provide a break in graphs. Today I experienced the next day’s column would not allow the deletion of the contents.
I get the … It’s now working normally! I just opened the calc spreadsheet to check the process details and it’s work fine. I had saved and closed the calc sheet prior to tackling this question. So, maybe that’s a work-around solution to the issue.
But what would cause this apparent issue, which I’m sure I haven’t come across before in many years for LibreOffice use? I don’t use cell protection, so what could cause this problem.
Is it a bug or is there some other explanation?