Lumia 1020 Unusable cause of lag unless there is at least 1.5g of free storage [WP 8.1]

[Eyes Pried Open]

My Lumia was just recently almost fill with music the other day. I had about 1gb of storage left on it. When I unplugged it from the computer it was actually unusable. The touch screen wouldn't respond at all. I have since then made sire I have 2gb of free space and it works great. Even with 1.5gb its usable bit still lags sometimes. Is this an 8.1 bug or is this what usually happens? I should've got a WP with expandable storage but the camera was such a selling point for me.

 

[bijak_riyandi]

never filled up my 1020 so far...

honestly, I'm not really sure that space in the storage affects the phone's performance THAT much