Well, i hope this doesnt continue long for you, it is either most likely in my opinion drivers or a tf2 bug with your hardware. hopefully both will get updates over time. You can try to use older drivers for that card as it has been out for a while and often times ATI will release drivers that are not necessarely better than the old ones.
It seems to me that if the textures come back after the steam comunity event that somehting is messing them up and they are just 'stuck' in that state untill they are told to be reloaded (or something). Not quite sure on this one - other than trying 2-3 driver versions, check for overheating, and ensure that everythign is up to date.