Cannot place levers and buttons on extended piston base

Do you try/want to place the button on the side of the piston?

Yes.

You can place levers and buttons on unpowered pistons, but when the lever/button is powered (when placed on side (not include back), top or bottom, the attached lever/button it will break. See MC-93631.

I see. Well at the moment one could keep in mind that this is only possible as long as the attachment area is a 16x16. An extended piston doesn't have that 16x16 at its sides anymore.
However, that doesn't mean that it won't be possible, one day.
There are special cases such as the torch which can be placed onto smaller shapes, so hypothetically it could be possible, and Mojang plans to overhaul Redstone (and kinda lots, if not everything, step by step) anyway.

Mojang may make that decision one day if it should be possible for extended pistons, as long as it doesn't cause problems within the system, and brings majorly benefits.

In case this bugpost gets closed as Invalid/feature request, don't be sad or disappointed, I'm certain some Devs will take notice.

As restructuring often takes sometime, let's wait and hope for the best 🙂

For suggestions, please visit Minecraft Suggestions on Reddit or visit the Feedback website.

Quick Links:
📓 Issue Guidelines – 💬 Community Support – 📧 Customer Support – ✍️ Feedback and Suggestions – 📖 Game Wiki

Reopened, as similar tickets has been fixed in the past

Can I have ownership of this ticket?

Hi there!

I can confirm for release 1.16.2.

Resolving this as duplicate of MC-176481 since that appears to be the underlying issue and that report has already been triaged (while this one has not).