Do you mean the 1st URL hotspot disappears in the viewer when you add the second one? Please make sure the panoramas are in "actual size" mode rather than "best fit" when you set the URL hotspot. Otherwise the hotspot location may not be accurate on the pano. In order to make sure every URL works fine, please let current URL hotspot lose focus after editing, you can do this by just clicking other part of the pano with your mouse.
If it is not the problem you mean, please give us a more detailed description.