Some copied cells are missing when pasted

The closest post I could find to this problem is here, and my problem seems to be different. (and even more strange).

If I copy a selection of 5 cells from one row of a worksheet like this:
ScreenShot618.png
and then try to paste (either simple paste, or paste-values) several rows below, but shifted one column to the right, the last cell of data is missing, and the paste box surrounds only 4 cells!:
ScreenShot620.png
If I paste the same 5 cells in the same columns as the respective copied cells (i.e., several rows below, directly below the copied cells), the pasting seems to be fine:
ScreenShot621.png
While writing this post, I thought I'd experiment, and I found that pasting the cells two columns to the right also only pastes 4 cells, but rather than the last cell of data missing, it's the fourth out of five!:
ScreenShot622.png

Please, someone, tell me what on earth is going on here and how to fix it! I inherited the spreadsheet from someone else (with the data that I'm copying already in it. Even if I'm able to work around the problem this time, I'd really like to know what's happening because I'm afraid of it happening again. I didn't notice it happening this time (someone else noticed an error) and this could cause problems if it slips through.

Many thanks,
Paul