Probably due to the n-key rollover over USB. While Macs technically support it, the feature is not well implemented and can cause problems just like the one you're describing.
If you want to keep the TK, I would suggest purchasing a second-hand official Apple keyboard to keep on standby for when you need to access the recovery console or other utilities outside of OS X. Your other option, and the one I personally would pick, is to get rid of that keyboard all together and purchase something that's more
Mac friendly.