Where does the space go when sideloading an app on WP8.1? Is there any bug in Windows Phone??

[nitishnk]

the system memory shows 2.4 GB in the storage sense. Now when trying to install an app from file browser for ex- I was installing Asphalt 8.XAP which was 0.9 GB. I downloaded on my desktop and copied the same to my SD card on the phone. I tapped on this file. It took some time but could not be installed. Then the next thing I saw was increase in the size of my phone memory which bumped up by 0.9 GB and showed 3.3 GB. But the app was not installed. Next day, I found the option to install local apps in the store. There it showed up Asphalt 8 and i installed the same on my SD card. Then after opening storage sense, I found the app installed on my memory card. Still the system memory in the phone shows 3.3 GB. But in the Lumia Storage check it shows system memory as 2.4 GB only and the rest in others.... I tried the same trick with any apps and the phone system memory went on increasing. Currently it shows system memory as 3.8 GB. Where the hell this memory goes when tapping on the XAP?? Or its a bug?? Any body??