First Time Bars

I'm trying to use first and second time bars (Prima Volta). Having got the line from the palette, I have no problem getting the left-anchor sorted on the first note of the bars in question. However, I seem to be unable to stretch the line to bars beyond the first.

I CAN double click the line and drag it to the end of the 2nd of two first time bars but as you can see from the screenshot, the right hand anchor remains very firmly at the end of the first bar.

Even if I do manager the stretch to two bars, the extended line does not appear in the part - see 2nd screenshot.

Anyone able to advise please?

Thanks
David