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Okay, I think I've found the cause of the second rounding bug above: at the end of the bigcomp function there's a correction block that looks like
 ...
 else if (dd < 0) {
 if (!dsign) /* does not happen for round-near */
 retlow1:
 dval(rv) -= ulp(rv);
 }
 else if (dd > 0) {
 if (dsign) {
 rethi1:
 dval(rv) += ulp(rv);
 }
 }
 else ...
The problem is that the += and -= corrections don't take into account the possibility that bc->scale is nonzero, and for the case where the scaled rv is subnormal, they'll typically have no effect.
I'll work on a fix... tomorrow.