As the title says, the drop rate of wither skeleton skulls is way too high right now. I believe they are supposed to be a very rare drop, and I've gotten 7 skulls in the last 10 Wither skeletons that I've killed using only an unenchanted diamond sword.
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I am using version 1.6.0, and I am not enrolled in the beta.

I can confirm this, I play bedrock (windows10) mostly realms 1.6 not beta. I seem to get a skull at least 1/2 the time if not higher odds. I use a bow.
Thank you for your report!
However, this issue has been temporarily closed as Awaiting Response
Is this still an issue in the latest version?
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Cleaning up old tickets: This ticket had been set to 'awaiting response', but has not received a response from the reporter (~3 months+) so is being closed as Cannot Reproduce. If you feel this is still a valid issue then please comment, or create a new ticket following the Issue Guidelines which includes steps to reproduce the problem.
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Can you please confirm which version of the game you're using? Are you enrolled in the beta?