Excel chart in 2003 Word converts incorrectly with Adobe

I'm working on our school's accreditation proposal. I'm responsible for creating the self-study, which analyzes the test data of our students. I've created an Excel workbook with spreadsheets for each grade level test scores. From these scores, I've created an Excel bar chart from data in each of the spreadsheets. I've used the same process to create 10 different charts.

I have copied and pasted the charts into a 2003 Word document as pictures. Same process, same Excel bar chart properties - no problems. When I convert the entire Word document to .pdf, most of the charts display identically to the original Word document. But 3 of them have weird anomalies - 2 charts show really thick borders on the bars and 1 chart has the thick border around the entire chart.

I've worked the charts numerous times, but there isn't anything wrong on the Excel side. I've created just the single page in .pdf form, but each time, I get the same issue. Why would 7 charts in the same Word document convert correctly, but 3 display problems?

Regards,
Pamela