Isis template in Joomla 3.x breaks Hikashop menus

I'm using HS 2.1.2 in Joomla 3.1.1 and when trying to access Hikashop control panel in backend, its menu breaks totally and only displays menu text in h2 format but no links at all. I'm using default 'Isis' admin template

I switched templates to 'Hathor' and it works a bit better but still buggy: all menus/submenus display, but without any format. It displays a large unordered, nested list, without any format that overlaps all other content in page.

I managed to style Hathor to fix the menus but the result is weird and other extensions do terrible when using Hathor, in the other hand the only one that displays wrong with Isis is HS, if at least links worked correctly, it would be faster to fix css for Hikashop only.

Can you fix it, please?

I attach screenshots of both templates implemented for HS.

Thanks for your help

Thank you, it most probably happened because I upgraded from J1.5 to 3 and simply reinstalled HS and copy all info and settings