Yes I have noted this personally and seen many people report this symptom which I believe to be one of the symptoms of the ‘soft glans syndrome’. The shaft seems to become extremely hard and yet the veins and not bulging as (in my case) they usually do (when properly aroused or extremely horny). This rock-hard CC, is coupled in many cases it seems, with the deflated glans and CS and hence decreased sensitivity.
To illustrate how it happens to me: if, say, I start watching porn and immediately start touching myself and then masturbating as I become erect and continue constant physical stimulation, my penis will remain feeling ‘normal’. However, if I stop, even for a few seconds, I can distinctly notice that the shaft becomes harder, feels more compressed and is less sensitive (as well as the glans and CS deflating). Interestingly, from this point on, if I start masturbating again but do not have visual stimulation or am not paying attention to the porn (or sex or whatever) my erection will be maintained but will not recover from this compressed hardness.
From this point on there are two ways I’ve noticed return the penis to a ‘normal’ erection state.
1. If I am then properly mentally/visually stimulated, the glans will inflate and the shaft’s vascularity will noticeably increase and feel softer, but if I measure, it actually have increased in girth.
2. Stop all stimulation and all my erection to subside, down to 50 or so percent, before resuming stimulation (assuming it is sufficient)
As I have noted in the other thread, the ease with which this hardness of the CC and deflation of the glans and CS occurs is inversly proportional to how horny you are. It will happen less or even not at all if you’re really horny (depending on the severity of the underlying cause of this issue).