I am losing the format of a column when I ...

I'm using 365 On a Mac after upgrading from 2011. Lots of new things to ferret out here.

I am losing the format of a column when I do the following:

Setup:
Columns A and D are formatted as General.
I have a table of 18 names in Col A

Column D1 points to A1
Column D2 points to D2
Column D3 points to D3
etc. ...
By pointing each cell to the previous row, a cascading list of contents is created Column D1, i.e, the selection in A1 is propagated. This column D has 100 rows.

To change Column D, I double-click D1 and change =A1 to =A2 and a new cascading list of A2 is created.

Works great so far.

From here it goes pear-shape.

Alternately, I should be able to click on D1 to select a cell (i.e., currently points to =A1) and drag it down Column A to my next selection. When I do this, Column D turns all cells to a cascaded list of formula =A2.

I cannot undo this action. I feel that alternate is a preferred method vs altering a formula.

To recover, I again set up Column D1 to =A1. Forgetting that the rest of Column D is zapped, I dragged down 20 rows ending with a copy of Column A and "empty" rows of 19 and 20 with a zero on the left side of each cell. This is telltale in 19 and 20 in that the format is gone as a numeric value should be rightmost in the cells.

To confirm, I select Column D and call up Format Cells which shows the General setting is not set.

The preferred method above worked in Office for Mac 2011.
Are there any settings (Preferences in Mac: Options in Windows) that I should use to defeat this behavior?

Thx Mike

It would be helpful if we had a sample workbook. For example, I don't understand if this is like:
Column D1 points to A1
Column D2 points to D2 - a cell points to itself?
Column D3 points to D3 - a cell points to itself?
etc.

or

Column D1 points to A1
Column D2 points to A2
Column D3 points to A3
etc.

See the yellow banner above your post (at the top of this page) on how to attach a sample workbook.