On Ubuntu, perl 5.8.7 and on W32, AS Perl 5.8.8 my debug help says:

b [ln|event|sub] [cnd] Set breakpoint

On the linux box, man perldebug provides similar guidance. Are you sure about your b $var?

In any case, it occurred to me that setting the breakpoint to the line number INSIDE your ANONYMOUS sub would be worth trying.

And, lo and behold, doing so causes my debugger to behave as expected. I believe that since the sub is anonymous, we can't b sub_name (and, of course, the preceding line, calling the sub is not breakable).

Update: fixed square brackets