Spurious fire from timer

Question

*Question:* _Has anyone experienced the behavior, which I describe here?_ 

Posting questions here makes me think. This is a better version of <http://www.mathworks.se/matlabcentral/answers/65815-weird-behavior-when-debugging-code-invoked-by-timer Weird behavior when debugging code invoked by timer>. 

I argue that it happens that a callback is spuriously fired during debugging of code invoked by a timer. Now, I think I have a way to demonstrate the behavior; that is to reproduce the behavior.

Recipe:

# R2012a 64bit, Win7
# put a break-point in the subfunction, |index_out_of_bounds|, at line 7
# start the function, |spurious_fire_from_timer|
# at the break-point execute |stk1 = dbstack;|
# open an m-file in the editor
# at the break-point execute |stk2 = dbstack;|
# inspect the stack-drop-down-list
# run |whos| and |{stk2.name}'|
# click [Continue] (/F5) 
# run |whos| and |{stk1.name}'|


  K>> whos
    Name       Size            Bytes  Class     Attributes
    a          1x1                 8  double              
    stk2      10x1              4164  struct 

Note that stk1 is not in this workspace and display the function names

  K>> {stk2.name}'
  ans = 
      'index_out_of_bounds'
      'invoked_by_timer'
      'timercb'
      'timercb'
      'index_out_of_bounds'
      'invoked_by_timer'
      'timercb'
      'timercb'
      'wait'
      'spurious_fire_from_timer'

[Continue] shows

    Error while evaluating TimerFcn for timer 'my_timer' 
    Index exceeds matrix dimensions.

and takes us back to the first break. Now, stk1 is in the current workspace

  K>> whos
    Name      Size            Bytes  Class     Attributes
    a         1x1                 8  double              
    stk1      6x1              2582  struct              
  
  K>> {stk1.name}'
  ans = 
      'index_out_of_bounds'
      'invoked_by_timer'
      'timercb'
      'timercb'
      'wait'
      'spurious_fire_from_timer'
  K>> 

*Comments:*

* This shows that opening an m-file caused Matlab to fire a callback. 
* I think this can be triggered by other user actions as well. However, I'm not sure which or whether it is intermittent.
* While experimenting with this behavior yesterday Matlab once crashed "without smoke"; just dropped dead without any crash report. 
* This behavior does not occur (i.e. I failed to make it happen) with 'ExecutionMode' equal to 'singleShot'


*where* 

    function    spurious_fire_from_timer()
        tmr = timer('Name'      , 'my_timer'        ...
            ,   'TimerFcn'      , @invoked_by_timer ...
            ,   'BusyMode'      , 'drop'            ...
            ,   'ExecutionMode' , 'fixedRate'       ...
            ,   'Period'        ,  1                ...
            ,   'StartDelay'    ,  1                ...     
            ,   'TasksToExecute',  1                ...
            ); 
        start( tmr )
        wait ( tmr )
    end

and

    function    invoked_by_timer( tmr, evnt )
        index_out_of_bounds()
        variable_not_used( tmr, evnt ) 
    end
    function    index_out_of_bounds()
        a = 17;    
        b = 18;
        c = a(2);
        variable_not_used( a, b, c ) 
    end

and

    function    variable_not_used( varargin )       
    % variable_not_used - helps keep the code analyzer box green  
    end

Spurious fire from timer

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