In phpBB-3.0.6.zip the prosilver template at phpbb3\styles\prosilver\template contains an extra space not present in other versions (not sure which).

The extra space is on line 51 before tabindex="5":

		<dd><input type="password"  tabindex="5" name="password_confirm" id="password_confirm" size="25" value="{PASSWORD_CONFIRM}" class="inputbox autowidth" title="{L_CONFIRM_PASSWORD}" /></dd>

And causes mods such as AntiBotQuestion to be unable to match the line. Note that some templates based on earlier prosilver do not contain the space.