Yeah, it isn't right. In the very early WebGL days there have been a handful of implementation bugs where previous VRAM content was accidentally exposed in text

Yeah, it isn't right. In the very early WebGL days there have been a handful of implementation bugs where previous VRAM content was accidentally exposed in textures, but these things have been fixed quickly. AFAIK, most of this is now also taken care of down on the hardware and driver level.