Without seeing what's on the screen it's impossible to tell exactly what's going on. That said, that's normal behavior IF (as already mentioned) it's at the beginning of a sentence or if there was a capital letter already there...in other words, if you're deleting a capital letter, the shift key will automatically activate (again). To deactivate it simply tap the shift key.
Curious, why do you have a fake iPad signature on your iPhone?
Well the cursor is away from any letters or in blank space.