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Honestly, I had a gut feeling, tried swapping the index types, and it was fixed. Others then investigated the root cause.

Steem doesn't use this particular index so is safe.

I usually do a tracelog and see atleast which function/method caused corruption.May not work always.. and exception handlers sometimes gives information too. Another thing to do it keep watching stack/globals,buffers etc. You could see unexpected value, which could be an indication of corruption...Which language is this written c++ /c#/go?