NV ForceWare system freeze due to texture memory fragmentation

While preparing the Games Convention game demo, I’ve encountered a strange but (quite luckily) reproducible system lockup caused by keeping our main character VBOs and textures in OpenGL video memory for reducing the loading times. Removing the character and reloading it on each level switch solved the problem. On ATI, there is no lockup and things just work. Has anyone else encountered such issues (esp. in play-time texture streaming scenarios)?