id=”email” is hiding email field in comments

I can’t get the email input field to show up in my custom theme.
I have narrowed it down to id="email" hiding the field for some reason – if I replace this with id="author" for example, an input field shows up. Is id="email"deprecated?
All localhost at moment, so can’t link to site.
Here’s the comments.php code in question – author input field shows fine:

<p><input type="text" name="author" id="author" value="<?php echo esc_attr($comment_author); ?>" size="22" tabindex="1" <?php if ($req) echo "aria-required='true'"; ?> />
<label for="author"><small><?php _e('Name'); ?> <?php if ($req) _e("(required)"); ?></small></label></p>

<p><input type="text" name="email" id="email" value="<?php echo esc_attr($comment_author_email); ?>" size="22" tabindex="2" <?php if ($req) echo "aria-required='true'"; ?> />
<label for="email"><small><?php _e('Email (will not be published)'); ?> <?php if ($req) _e("(required)"); ?></small></label></p>