You may have a bod keyboard, or it could be just one of those things. Firstly what is working normally: the keyboard layout you are using has something like meta sends escape and has mapped a meta key. It could also be alt sends escape, but I don't think so. What is meta? It is the fourth shift state (the first three are shift control and alt). The most common choice for a meta key is either one of your alt keys or the windows key. Now what went wrong? You lost a key release event. The way keyboards work is for every letter typed you get two events: a key press and a key release (there is also a key repeat that you get when you hold a some keys but not shift keys). Capital letters needing a shift state have four events, for example a capital A would be shift press,
a release, and shift release. Similarly for control alt and meta shift states are entered on key press and left on the corresponding release. So with the symptoms you were seeing you probably lost a key meta release. This could be electrical noise, a bad keyboard (if it happens frequently and could just be a sticky key) or a software bug. If it is a software bug it is oft caused by context switches between multiple parsers of key events with inconsistent use of shifts during context switches. For example, if your window manager uses alt tab to switch windows and you use it to switch either to or away from vnc and use the mouse to go the other way your alt shift state may become confused on the remote machine, or in this case if you used meta-alt-f7 to switch to X and ctl-alt-f1 to switch back, the text console would have seen an extra control release which it ignored, but not seen the meta release. or your meta key is stuck.