I edit a large amount of product photography and I used to use the patch tool frequently to fix areas that needed cleaned up that had some sort of detail. Below you will find an image I was correcting and the result. I was not trying to get rid of the little nub, just replace it with one that looked better.
I tried to use the content replace tool as well and it not only changed the area I was trying to correct but the part I was taking from. It also left a weird shape around the part I replaced. See images below.
-original -after replace tool
I can confirm what the others have said. I was able to do a very quick patch with the regular patch tool in Normal mode.
The Content Aware mode is for something different entirely, when you want to give Photoshop more freedom to make believable looking stuff up from other parts of the image.
The first set of images was using the patch tool in the normal mode. That didn't work, so I was just experimenting with the replacement tool. Call me a stick in the mud but I like the patch tool in CS5 better. It doesn't over smooth things or create artifacting and it allows me to retain the details that I want. Sometimes in tight areas the clone tool just isn't practical.
Certainly doesn't look like it's working right in your second example, but that's not the result I got at all.
I'm going to assume you know how basically to use the tool - that you'll need to drag to a similar part of another nub on the plastic.
Funny thing was the second time I tried it I couldn't get as good a result as the first time - it seemed to want to make the nub too dark. Only thing I had changed was the feathering of the Polygonal Lasso tool - I had reduced it. Then I did the same in Ps CS5 and was not able to obtain a good result either.
I did some more experimentation and I found that the best results are obtained with the Polygonal Lasso tool set to have some feathering - 2 or 3 pixels in this case. Is it possible you're seeing a difference between how you have that tool set between PS CS5 and PS CS6?
I kind of prefer the Healing Brush tool for this kind of work myself.
I will play with it some more, I guess I expected it to work the same out of the box as the old version.
I have just grown accustomed to using the patch tool because most of what I edit has some sort of repetition. It is often faster/easier for me to pull from an area that looks good instead of painting something in.
It's possible it's broken specifically on your particular system, and maybe you need a video driver update to make it work properly. This version uses the display pretty differently than its predecessor, which means it may be uncovering a bug in your driver.
I've found the new patch tool to one of the success stories in CS6, and find it works rather better than CA Move. But as a regular user of the old patch tool, you will know that when correcting against an edge, you need to overlap both sides of that edge with the initial selection, and slide it along the edge to keep it aligned. With the limited source pixels alongside your example, you would probably need two stabs at it.