Need to send a key up, silly.

src/video/uikit/SDL_uikitview.m

@@ -304,6 +304,7 @@
 - (BOOL)textFieldShouldReturn:(UITextField*)_textField
 {
     SDL_SendKeyboardKey(SDL_PRESSED, SDL_SCANCODE_RETURN);
+    SDL_SendKeyboardKey(SDL_RELEASED, SDL_SCANCODE_RETURN);
     [self hideKeyboard];
     return YES;
 }