I'm not necessarily suggesting they intentionally made the dll different for RE. The possibility that RE was maliciously backdoored is certainly possible, but there are three plausible other possibilities I can see:

1. A bug was introduced that affects both, and the bug never make it back into the 11 branch

2. There's conditional logic in RE that triggers the issue

3. 11 introduced new behavior that never make it to RE, causing the bug

The fact that 10 is seemingly unaffected is telling. #2 seems very unlikely, because it suggests new conditional logic was added and not tested. #3 seems unlikely because I can't understand why the binaries would be different anyway. #1 seems unusual because it suggests there's no canonical source of truth for the code, which feels very unlikely for bitlocker of all things (where you want everything speaking the same language).

If there's any benign explanation, I suspect it's likely due to incompetence. This feels like such a strange problem to have. I suspect the follow-ups you suggest are going to happen very soon and we'll know more.