There seems to be a problem with falling through "jump-thru" platforms. I even tried using the default platformer template (unchanged) as a new project, and I still can't fall through the "jump-thru" platforms even in that.
I also tried using Chrome (Version: 23.0.1271.95 m), Firefox (Version: 17.0.1), and Internet Explorer 10 (Version: 10.0.9200.16438), and it's still not letting me fall through the "jump-thru" platforms (the blue colored ones in the default platformer template), and I'm pressing the down arrow too like it's coded in the event sheet from an unchanged version of the default platformer template.
Falling through the "jump-thru" platforms works for me in r110.2, though.
I'm using Windows 7 (64-bit), and my graphics card is a NVIDIA GeForce GTX 560 Ti. The driver date is October 2012 (2 months old (306.97, the latest version)).
I also got this error below, while running the default platformer template (unaltered) in Internet Explorer 10 (Version: 10.0.9200.16438). No third party plugins or behaviors were being used.
<img src="https://dl.dropbox.com/u/20404296/error.png" border="0" />
Here's what the error message said just in case the picture above doesn't show up for whatever reason (due to website issues/problems, me possibly removing the picture from my dropbox at a later date, and etc.):
"Message from webpage
localhost/, line 1 (col 9)
This is either a bug in Construct 2 or a problem in a third party plugin or behavior - please report it to the developer!"