1.11 doesn't fix this issue anymore than 1.1 did. 1.11 fixed very little client issues, it affected server issues mostly and this problem is a local issue.
It's nothing to do with skins (unless someone is so out of it that they still run 1.0 - there was a skin issue in the original game that was fixed in 1.1).
The fix has been mentioned above (type vid_restart in console) but this will only fix it for players who cannot see someone, it won't make you visible to them if you do it.
It's a local graphics bug that prevents the graphics from loading on a level load and it's very random.
If someone complains to you about you being invisible advise them to type vid_restart in the console. If they don't know how to do that tell them to reconnect to the server.
Either will reload their video settings and refresh your model to them.
hmm..i used to run custom skins and weapon skins. i had this problem then. i removed all of those and i dont have it happen to me anymore. coincidence prolly.
Yeh, I'm pretty certain 1.1 removed that bug. 1.1 forced all custom skins to show as the default stock skins (american army and german army - can't remember the actual names).
This graphic bug is entirely separate but your fix was right, if only client-sided (although it's a client-side bug, so that's cool).