I've noticed a couple of issues with preview:

• Hovering over a factory that is in the location of the preview window results in the preview window toggling on each tick. I believe that if the preview window can be drawn in a way where it does not block the cursor 'seeing' the factory building beneath it, that will prevent the flicker.

• Factory contents within the preview are not correctly updated in some situations. Grabbing one building from inventory shows the preview, but then if you grab another building without first clearing the cursor, the preview will show the grid of the second building (concrete pattern changes), but the contents of that building will still reflect the previous one. This issue presents any time the game changes the preview contents without toggling the preview (i.e. the next tick). If you walk into a building while the cursor is previewing that building, and then once in the building, your cursor is now over a building within that one, the preview will to the same thing just described.

The above led to some confusion until I got a handle on the bugs, especially when cycling through buildings to find the desired one to place. Clearing the cursor (Q) between grabs is a workaround for the moment on that one.

Hm, interesting. I've reported this as a vanilla bug. Thanks for the report!

Okay, the issue is fixed in Factorio 0.15.11.

The hover/update issue is indeed fixed in 0.5.11, but the flicker issue is there. It's most prevalent on smaller / narrower displays, as the preview is closer to center and you are more likely to be hovering over a factory in the same location as the preview.

You can adjust the size of the preview in the mod settings (Options -> Mods -> Per player). I've sent a feature request for an intangible GUI node though, that should help with this issue.