Yes, it looks likely it's an ESP8266 bug (however that's a lot of data to be leaked - are you sure you're not running other code as well?)
Please can you post this in the ESP8266 forum and carry on there? You're more likely to be able to get help there as I don't know the internals of the ESP8266 port that well.
Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
Yes, it looks likely it's an ESP8266 bug (however that's a lot of data to be leaked - are you sure you're not running other code as well?)
Please can you post this in the ESP8266 forum and carry on there? You're more likely to be able to get help there as I don't know the internals of the ESP8266 port that well.