Do you see the same problem when you start Emacs using
emacs -Q (no init file)? If not then recursively bisect your init file to find out what is causing the problem (e.g.
*Backtrace* seeming to disappear and Emacs becoming dysfunctional).
If you still see the problem with
emacs -Q then consider reporting an Emacs bug.
*Backtrace* has not been killed then you can visit it again (
C-x b) and then write it to a file using
C-x C-w. (Since it is not visiting a file there is no autosaving or backup file produced for the buffer.)
[Your question is anyway unclear in some respects. Specify what exactly you mean by "emacs becomes dysfunctional", for example.]