What could cause the user hover menu to fail to completely render?

i have noticed that in elgg 2.3, the hover menu for users on my site's main activity page does not open properly. it's frame appears but it's contents never load.

i have found that this is in some way being caused by my own plugin 'filter and sort' - but the strange thing is that i have pretty much commented out every single line in that plugin, while keeping the bare bones necessary just to load a plain activity list.. and the problem remains. i have stopped all JS loading from that plugin and stopped all views being over-ridden and i am still no closer to finding the cause of the problem. there are no errors in the browser console or php log.

anyone seen this before?