It would be interesting to try it in v2 and see if it works. Maybe export your menu and send it in an incident to WebAssist support. They could then try it in both v1 and v2 to see if it works in v2 or if they can find a fix for v1.
V2 uses a slightly different menu structure, which may fix this problem but I couldn't be sure without testing. I can't seem to get it working on your page by manipulating the css alone, but that doesn't mean I didn't miss anything.