I confirm it now works again.  Thank you!

Yeah, I definitely broke it.  I need to think about the proper way for the debugger to move around in the call stack.  I thought it was working, but it is definitely completely broken.

In debugging mode, dbup and dbdown do not seem to work as expected. In this example:

%%%%%%%% testdb.m %%%%%%%%
function testdb
  val = 0;
  a;
end

function a
  val = 1;
  b;
end

function b
  val = 2;
  keyboard;
end

Octave's behavior is:

octave> testdb
stopped in /opt/octave/testdb.m at line 13
13:   keyboard;
debug> dbstack
stopped in:

  --> testdb>b at line 13 [/opt/octave/testdb.m]
      testdb>a at line 8 [/opt/octave/testdb.m]
        testdb at line 3 [/opt/octave/testdb.m]
debug> dbup
stopped in testdb>b at line 13 [/opt/octave/testdb.m]
debug> dbstack
stopped in:

  --> testdb>b at line 13 [/opt/octave/testdb.m]
      testdb>a at line 8 [/opt/octave/testdb.m]
        testdb at line 3 [/opt/octave/testdb.m]
debug> dbup
stopped in testdb>b at line 13 [/opt/octave/testdb.m]
debug> dbup
stopped in testdb>b at line 13 [/opt/octave/testdb.m]
debug> dbdown
error: dbdown: invalid stack frame
error: called from
    testdb>b at line 13 column 3
    testdb>a at line 8 column 3
    testdb at line 3 column 3

while in Matlab:

>> testdb
K>> dbstack
> In testdb>b (line 13)
  In testdb>a (line 8)
  In testdb (line 3)
K>> dbup
In workspace belonging to testdb>a (line 8)
K>> dbstack
  In testdb>b (line 13)
> In testdb>a (line 8)
  In testdb (line 3)
K>> dbup
In workspace belonging to testdb (line 3)
K>> dbstack
  In testdb>b (line 13)
  In testdb>a (line 8)
> In testdb (line 3)
K>> dbup
In base workspace.
K>> dbup
In base workspace.
K>> dbstack
  In testdb>b (line 13)
  In testdb>a (line 8)
  In testdb (line 3)
K>> dbdown
In workspace belonging to testdb (line 3)
K>> dbdown
In workspace belonging to testdb>a (line 8)
K>> dbdown
In workspace belonging to testdb>b (line 13)
K>> dbdown
In workspace belonging to testdb>b (line 13)