Currently, the bind for taking replays/demos in ET only starts recording. There is no corresponding button to turn off demo recording. Here is a script you can use to start and stop demo recording AND preserve the naming structure in the current record demo function:
set demoon “autorecord; set nextdemo vstr demooff; echo ^4Recording ^7demo”
set demooff “stoprecord; set nextdemo vstr demoon; echo ^7Recording ^1stopped”
set nextdemo “vstr demoon”
bind x “vstr nextdemo”