changing linestyle of segments single XY graph creates multiple legend values

[jaapl]

I have a scatter plot with a single curve consisting of n datapoints. The corresponding legend is the name of the dataserie assigned in a cell.
When I manually change the linestyle of 1 or more line segments of this curve from a solid line to a dashed line, the legend contains suddenly n entities with names corresponding with the x-value of each data point.
When I repeat this in another graph with multiple scatter line curves, the legend name of that particular data serie stays the same. This problem occurs consistently in each XY graph with a single data curve in my workbook (Excell 2010). In graphs with multipe data, this problem does not occur.

Is this a bug in Excell or is there a way to correct this?
Of course I can remove the legend and replace it with a text box with text and a colored line or create multiple data lines to circumvent my problem , but I really like to find a working and simple solution for this.

Thanks in advance for your assistance.

Jaap L.