Version of Premiere is 2014.0.1. The more I think about it, I think this must be a glitch.
One more thing worth mentioning: Every time I pressed Enter after entering the timecode it would start playing my timeline from the beginning. I realized that the Enter key is a default shortcut to render and play the sequence. So I disabled it in the shortcuts.
Basically I just want to be able to quickly type + or – and the number of frames I want to move the playhead, like in FCP, without having to use the mouse.