Yes, this is a known gotcha of the bind variable emulation and would still be a problem if PG handled bind variables itself, if you think about it a bit. For PG would still treat the bind variables as being a string when doing its overload resolution.
The value of using bind variable emulation, beyond being able to share queries with Oracle when they're SQL92 compliant, is that it defeats attempts at SQL smuggling.
How to fix it? Can't, really.
