"NetRanger" on the Opus forum at hydrogenaudio recently posted a build of opustools/opusenc that includes a fix for a bug described by Opus developer J.M. Valin as being "...an issue with digital silence on x87 FPUs (so mostly just 32-bit x86). The issue was already present in previous versions, but it only happened when delayed decision was on (which was only implemented in the latest opus-tools)." A poster there described the issue as causing a noticeable high frequency loss at the beginning of certain "problem samples." The NetRanger build with the fix for both win32 and win64 versions can be downloaded here:
https://hydrogenaud.io/index.php?action=dlattach;topic=116746.0;attach=14615