If it has been one full year, then it is extremely unlikely that the culprit is among the patches of the Cool SL Viewer which went through v1.20 to v1.23 during this period, with different sets of patches each time, and none affecting the inventory before v1.22 was out (at which point the "Worn" tab was added, but can't affect the inventory in this manner either)... Beside, you are the only person to report such a problem, so I'd tend to consider that you simply spend much more time with the Cool SL Viewer than with any other viewer and therefore only see the problem occurring with the former but actually do have a corrupted inventory issue...
To be sure, just switch to another viewer for a while, and see if it happens with it too... If it does happen, then you have a definitive answer (and if you use the official viewer, you can tell Lindens that there is actually an inventory issue on your Av(s), and get them to fix it). If it doesn't happen at all with the official viewer, then it's a pure mystery...
Oh... this issue could possibly be network related too... Try reducing the MTU (it defaults to 1500, but most ADSL links will not allow over 1492 and this can result in many lost or corrupted packets, especially with UDP). To be on the safe side, I set mine to 1400 (ifconfig eth0 mtu 1400)