Possibly a bug, more likely operator error.

[Ronwoodson2]

In the attached file I create a half inch circle then cut vectors to make a top and bottom semicircle.
I copy them along the polyline then align them to the polyline, move the top row a half inch to the right.
If I'm not missing something, they should align and connect using the connect vectors icon. I selected all semi-circles but only half of them connect. There is a .0167 inch gap between the pairs.
I tried the same process using the same settings--I think- in Version 9 and everything worked as expected.
Has anyone else had this issue?

[Adrian]

Not sure how you did it but I used the Array Copy tool to create a line of semi-circles 1/2" apart, I then used the mirror tool to create a flipped copy, aligned both to the line (giving a row of circles), move the bottom row 1/2" to the right, selected everything apart from the line and pressed J to bring up the join tool and it all aligned perfectly.

[Ronwoodson2]

Thanks, Adrian. I retraced my steps and I think I had somehow checked 'force even spacing'.
So I think it was operator error