Could you tell me which version of Kornitop you are using? If you are using any version prior to 0.7.0.1 this problem is to be expected.
Kornitop 0.7.0.1 fixes this behavior.
See: Kornitop development news
"1. Bug fix related to the "Sleep" functionality. This caused memory related crashes especially when used with Microsoft Office products, in particular Excel, where frequent copying and pasting is common."
