"We can't do that to a merged cell" error in non-merged cells

I'm encountering an error which reads "We can't do that to a merged cell" when I'm entering data into cells which are not merged. There are merged cells in the worksheet which reference the data cells, but what's unusual is that I'm not getting the error for every data cell. If I just select "OK" it enters the data fine and the linked formulas work properly, it's just kind of frustrating to have it pop up at seemingly random times.

Has anyone else encountered this? Any idea as to what causes it and what might fix it?

I've attached an example spreadsheet. The only thing the cells prompting the error have in common is that they're all for "Cmpd 2," which correspond to the bottoms of the merged cells in columns B through G. But not every "Cmpd 2" data cell does it. For instance in the example sheet, if you begin entering data into cell I2 and continue down the column, you'll first encounter the error at cell I9. From there down it will pop up every other cell. I can't tell what's different with cells I3, I5, and I7 that they don't produce the the error, and I don't know why "Cmpd 1," cells which correspond to the top of the merged cells in columns B through G, would not do it compared to the "Cmpd 2" cells that do it. I'm a bit perplexed.

Sorry if that description is a bit confusing, but if you open the example spreadsheet and start entering data in the highlighted cells you'll see what I mean.

Edit: Updated my Excel version

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Still using XL2003 as indicated in your profile?
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Thanks