Something broke Markdown tables with column alignment in the Markdown preview shown below the editor

Question

This is Ham Vocke's demo table with aligned columns:

| left | center | right |
|:---- |:------:| -----:|
| One | Two | Three |

This is it, rendered:

left	center	right
One	Two	Three

In the Markdown preview shown below the editor, the words appear one after the other, as if the Markdown contains:

left center right One Two Three

This is the same table without alignment, which appears correctly:

| left | center | right |
| ---- | ------ | ----- |
| One | Two | Three |

left	center	right
One	Two	Three

If you follow unaligned columns with aligned ones...

| left | center | right |
| ---- |:------:| -----:|
| One | Two | Three |

...it renders like you had written this Markdown instead:

center right Two Three
| left |
| ---- |
| One |

• Aaron Bertrand: Here? Stack Overflow? Somewhere else? Everywhere? Questions only or both questions and answers? New ask page?
• VLAZ: @AaronBertrand I don't seem to have access to the new ask page anywhere. But I can reproduce it for both questions and answers on MSE, SO, .SE sites (tried Worldbuilding and Sci-Fi), SU, SF, and StackApps. I think that covers most types of sites - both with special name/domains and generic ones. All in the old editor. EDIT: also tried the new editor here (on MSE): i.sstatic.net/Jf9PJ7D2.png
• balpha: My fault. I'm on it.
• Michael come lately: @AaronBertrand I found it when editing my hardware recs answer on dynamic-keycap keyboards, where I removed the alignment because I couldn't see what I was doing.
• philipxy: Apparently you are using other working markdown to show what the bug output looks like, but please say so explicitly, because otherwise you force every reader to look at the markdown of this post to see whether you are doing that.
• VLAZ: @philipxy well, you can't really show markdown in a post, when the bug is only in previews. It could have been a screenshot but it's less accessible. Since the preview only showed the word stripping any table formatting, I don't see the issue of showing only the words without table formatting.
• philipxy: @VLAZ We don't know whether the poster relied on the bug to produce the output, which would be bad since it spoils the question when the bug is fixed, and it might be fixed, so as readers & curators we have to look at the markdown. I didn't say the problem was not using the bug, I said "you are using other working markdown to show what the bug output looks like, but please say so explicitly" & I said why. PS I'm all for "using other working markdown to show what the bug output looks like" when possible, just because it is more accessible than an image. And for ALSO EXPLICITLY using the bug.
• VLAZ: It's a bug only present in the preview. We do know that it's not used in the post because that's not a preview. Unless you want to say that OP is bold-faced lying to us and the bug is actually present in any post, not just in the preview.
• Michael come lately: @philipxy There you go.
• philipxy: @VLAZ My only interest in actually manifesting the bug is simply basic bug reporting. Your comments don't seem very connected to what I actually have said. I'm done.
• balpha: @philipxy My 2ct as the primary recipient of the bug report: This is a perfectly good bug report that clearly described the problem and was easy for me to reproduce (and confirm the fix!).

Answer 1

Fixed now, thank you for being observant!

The other day we fixed an issue in the table validation code where things might be considered valid that shouldn't be. Unfortunately that ended up considering things not valid that should be.

I hope we've found the correct middle ground now 😁