I could not reproduce your bug on the latest 4 versions of AE I have installed. What is your OS and AE version down to the last decimal point? Is your version of AE up to date?
You may want to reset your preferences:
- Press Ctrl+Alt+Shift (Windows) or Command+Option+Shift (Mac OS) while the application is starting.
Resetting preferences seems to have worked. (Apparently, trashing the prefs isn't the same as resetting?)
For what it's worth, I'm on After Effects 18.104.22.168 & Mac OS 10.12.6
Both good steps when AE Starts acting wonky.
I have the same issue just after I was trying to type a degree symbol, maybe the wrong combination of keys could generate/replicate this error.
Resetting Preferences fix this for me.
I'm on After Effects 15.0.0. & Mac OS 10.11.6