As I've already suggested elsewhere, I think that rhythm may change the way a sentence is produced and perceived.
Glad, he accepted the appointment
makes me uncomfortable
Conversely, I would more readily accept something like :
Glad as never before, he accepted the appointment.
The difference here is the length of the initial adjectival phrase. Somehow I feel the former is too short (1 syllable), it's "not worth the comma", so to say. Might be just me, though.
I'm aware surprised is just a tiny bit longer, but it might make a difference.
I'd also like to add that this kind of initial AP, can sometimes explain why the subject is acting in such or such a way. I think it's the case, for instance in....
Tired, he went to bed.
I strongly sense "because he was tired" behind that one.