P: EPS or PDF Smart objects render badly (with jags) when being scaled or transformed.

No, this is not that problem as you appear to be talking about Smart Objects created in Photoshop and not placed eps, ai or pdf. 

There seems to be a misunderstanding about the results of multiple resamplings as opposed to a single resampling. 
And Smart Objects are supposed and intended to apply all of an instance’s cumulated transformations to their original content in one single operation. 

The preview in the Image Size dialog is effectively irrelevant and can produce results that differ from the actually scaled layered file even with no Smart Objects involved. 

Hello Every one it seems that the problem is back again in photoshop CC2017
I have trouble with resizing smart oject with transform compared to a rasterized layer
The transform preview is OK but the result is Jaggy !!

(The smart object itself contains only rasterized elements)

You have the same result when using "resize" and "export as" with a resize inside, "save for the web legacy" with resize inside go smooth ...

Thanks for looking into this. I have emailed a link to the files hosted in dropbox. The assets include the InDesign document, and examples pasted into Photoshop CC 2014 and into CS5, as well as a PDF from the document. The PDF is made without image downsampling. Pasting into Photoshop or rendering the PDF both give the same results in CC, which makes sense as the clipboard format from InDesign would be PDF.

Note that, I read in several other threads a quick fix for users who had pasted a smart object without anti-aliasing turned on can later invoke it by hitting transform, making sure anti-aliasing is checked and hit return. If I open the CC PSD into CS5 I can use this trick for force anti-aliasing on the paste done in CC. This trick does nothing for the image component in CC 2014.

Hi Angus,

I'd like to try to track this down. Could you send me the original InDesign file that shows the issue when pasting into Photoshop? My e-mail is jrubbo AT adobe DOT com.

Both were initially set on their default, so CS5 was bicubic and CC is bicubic automatic). For the sake of testing all scenarios I later changed CC to bicubic only but this makes no difference when pasting the smart object at 100%. My ramble above may have got a bit confusing but the sample image above is produced by 1. Place an image in InDesign, 2. scale, 3. copy 4. paste at 100% into Photoshop. The general interpolation settings made no difference for placing at 100% or for scaling the smart object. When you transform a smart object the only option in the tool bar is anti-alias on/off unlike a bitmap which will show different interpolation options. So from my tests CC is just ignoring the general settings and the local anti-alias option for the raster part of pasted smart objects. Hopefully someone can take these steps and verify the result in CC is the same with anti-alias checked on or off, while in CS5 checked on actually does it's job.The result in CS5 checked OFF is the same as CC checked on OR off. The problem is the same opening a PDF into CC 2014. In the open dialog choosing anti-alias on or off makes no difference to the image part of the PDF only the vector parts. In CS5 it is smooth. Even if someone only has CC or CC 2014 they could hopefully verify that side of the behaviour at least 🙂

What are you Image Interpolation settings (under Preferences>General...)? It looks like bicubic sharper (as a result of having Bicubic Automatic enabled) on the right and Bicubic (the default setting in CS5) on the left.

Did a lot more testing. The example sample above was an image placed in InDesign and scaled and then copied/pasted into Photoshop CC 2014 at same size as InDesign layout. The placed image renders without anti-aliasing even when the checkbox is on. If I do the same thing with the image unscaled in InDesign the pasted image is clean, and looks equal in quality to the original image placed in InDesign. However if I scale this 100% smart object in Photoshop CC 2014 it looks jagged just like the sample on the right above. If I open the original image into Photoshop and make it a smart object and scale it it looks fine. The problem seem to be with smart objects containing raster data that come via a copy from InDesign etc, my clipboard is default clipboard setting of PDF in both Illustrator and InDesign. I cannot imagine my colleague and I are the only ones with this issue? As it stands I cannot use Photoshop CC or 2014 at all for this work. Back to CS5!

Here's an image of the problem. Showing CS5 vs CC.

Just an extra note, if I copy from InDesign CC to Illustrator CC and then copy that to paste in Photoshop CC the image part is correctly anti-aliased as per CS5. But not directly from InDesign to Photoshop.

OK, but I've just verified this with a colleague who is using a different computer and Yosemite and he sees the exact same result. CS5 the pasted image is anti-aliased as expected but in CC or CC 2014 the image is not. I copied an image and a vector logo in the same object and the vector is fine but the image is not. The image result is the same with the checkbox on or off in CC 2014.