Summary, if anyone's confused:

March 16, 1999 - Game launched, meditate functions the way it does now on P99. You have to open the book and click the meditate button every time regardless of level.

October 28, 1999 - Characters level 35 and above no longer need to open the spellbook and click the meditate button to meditate. Just sitting without the spellbook will give the additional mana regeneration rates as long as you're the appropriate level.

August 23, 2000 - They added the /meditate command, so that character below level 35 can open the spellbook and instantly start meditating without having to click the button.

August 30, 2000 - They figured out a better way to implement the above, so now instead of having to macro the /meditate command, all you have to do is open the spell book and the meditate button is already clicked. Again, this really only applies to sub-35 characters. The /meditate command is now removed.

I don't think the way in which P99 is handling these patches is set in stone or known yet. Someone mentioned in another thread that level 35+ meditating without the book was planned to be in from the beginning, but I have no idea if that's true or still the case. You could try asking a level 35+ caster on Green or Teal if that's currently in the game.

I just hit level 35

Can confirm as of this post. I am meditating without my spellbook open or the meditate button clicked. I'm also gaining meditate skill.

Yeah, I'm getting this bug too. It doesn't seem to block my entire screen.

yea for the full classic experience you should not be able to see anything while meditating emulated how much focus it is required to regain mana in real life.

Not a bug. People ask Rogean before green started to make spells window smaller. If you go back like a month or 2 ago he shows the spells windows with meditate on it .