> I have no setting in PERLDB_OPTS that could explain this:

> $ echo $PERLDB_OPTS

> Why is the debugger behaving this way when run on a program in the current directory?

Did you also check for a .perldbrc .perldb rc-file in the directory?

Edit: see perldebug#Configurable-Options

update

For the records, seems this was the root cause:

see Re^3: perl -d: puzzling behavior when run in program in current directory