Sorry, someone tweeted me something strangely similar to your report and I got mixed up. We deal with a lot of bug reports coming from all directions and some users try to step in to, er, "help", so it can be pretty chaotic sometimes. I am sorry if for some reason this offended you.
I have further investigated the issue and I observed a leak, but I believe my measurements prove the bug is in Windows Phone 8.1, not Construct 2. The following screenshot shows my results:
https://dl.dropboxusercontent.com/u/15217362/wp81leak.png
The blue line which indicates a very slow leak is the process total memory, as in the total memory used by the operating system for the app. I took three snapshots over a period of about 19 minutes and all three of them indicate exactly 6100 Javascript objects using 4.23mb of memory. This appears to prove there is no memory leak in the Construct 2 engine, and is further supported by the fact the app does not leak memory on any other platform despite using the same engine. I think you will have to pursue the issue with Microsoft.