I just upgraded to Blender Version 2.78b and I ran into this problem. Note this may not be related to the version change but I have never seen this before and I have been working with Blender for several years.
Attached is a blend file to demonstrate the problem: http://pasteall.org/blend/index.php?id=45534
In the file I have a chain link that has an Array Modifier and a Curve Modifier. In 3D view this looks fine. The chain follows the curve and is sized appropriately. But when I change the method of display in 3D mode to Render from Solid, the Chain Links grow in size (puffed up cartoonish appearance). This also happens when I hit F12 to render the scene. Return to 3D view and all is well! Weird.
Any assistance that you can provide will be greatly appreciated.