I understand your frustration with the issue you're encountering. What you're experiencing is not necessarily a bug, but rather a common scenario when dealing with autogenerated content like charts in Word.
When you insert a chart in Word, it embeds an Excel worksheet to store the chart data. Each time you create a new chart, even if it looks identical, Word generates a unique underlying data structure. This unique structure includes metadata and possibly slight differences in how the chart data is stored internally.