I can't see the problem. Such "action at a distance errors" (i.e. the strange effects you observed when deleting some seemingly unrelated lines of code) remind me of my days as a C programmer. This more than anything else makes me take the possibility of a bug in DBI more seriously than I would have otherwise. That said, 9 out of 10 times I think I may have found a bug, it turns out that I'm the one who's wrong, so I've learned to be cautious about jumping to that conclusion.

I'm sure you'll get better ideas, but when faced with a stumper like this, my first instinct is to step through the rough patch inside perldb, and try to localize the error as much as possible. The error appears to be happening during the execution of the call to selectrow_array; in my copy of DBI.pm that function is implemented in Perl, so you could step into it and see exactly where the error is triggered. This may give you a clue.