Why does pasting into an unprotected cell in Excel protect it?

While researching the answer to this question, I stumbled across a rather odd behavior in Excel related to unprotected cells in protected worksheets.

To see what I mean, create a new workbook, unprotect its first cell (A1) and protect the worksheet. The only cell that text can be entered into now should be A1. Next go to some other application (for instance your browser) and copy some text from there. Select the first cell by clicking it once (don't double-click or paste into the formular bar) and paste the text into it.

Not only will this potentially change the formatting of the cell, it will also set its protected flag. Thereafter, there is no way to ever change that cell's content again without removing the worksheet's protection (or undoing the paste operation, of course).

Why is that? Is this desired behavior or a bug in Excel 2010 (the version I used to try this)?

It is actually expected behavior (well expected by Microsoft, not necessarily by users) which is the good news. And there is a quite simple work around which is the even better news.

When you paste in a piece of formatted text the cell gets given the "Normal" style and then has the required formatting layered on top. The "Normal" style by default has protection set to locked. So this is why it is being applied.

The solution is to modify the "Normal" style. To replicate a solved version of this problem create a new workbook, then:

1) On the Home Ribbon in the Styles section right click on the Normal box and click Modify. Press the Format button and on the protection tab uncheck Locked. (Remember this only applies to this spreadsheet, but that all cells will now be unprotected rather than protected).

2) Select All cells, right click and choose format cells, and under protection check Locked.

3) Select A1 only, right click, choose format cells, and under protection uncheck locked.

4) Protect the worksheet

Now we should be back at the same point as the example in the question in terms of locked and unlocked cells but with a different Normal style.

Now when I paste text in from word or elsewhere the cell does not become protected.

The previous answer no longer applies to the most recent version of Excel 365. The current version of Excel 365 now creates a new style named "Normal 2" or whatever sequence number it needs. It applies the new style which is locked instead of the modified normal style.

Here is the solution for Excel 365. Select the range of cells that you want others to be able to edit. Then, go to the "Review" tab. In the "Changes" section click on "Allow Users to Edit Ranges". Click the "New" button. Your selected range will auto populate with an auto-generated title. Make any manual changes you want. If you want people to be able to make changes only with a password, you can enter it here. I prefer for people not to use a password, so I click on the "Permissions" button, then on "Add". I want anyone to be able to edit without a password, so I enter "Everyone" as the user permitted to make edits. If you understand permissions, you can select one user or a set of users who will be able to make edits without password. Then just click "OK" until all the windows are closed. Protect your sheet and you are good.