This is a very common position for a spider a week or so into post moult. I have a theory, but have absolutely no proof that this is the case.
I suggest that the joints are stretched to maximum regularly in order to settle/cure. It is less obvious in arborials as this is a much more natural position for them, but it is more noticeable in terrestrials because of the abnormal appearence of the spid... but, it remains speculation.
Most people are like clouds. The sun comes out when they f*ck off...