Well....they are all removable.
I don't know the guitar and the picture is deceiving...I can perceive a gap I guess but it doesn't appear 1/4 or anywhere near 3/8 of an inch....I'll take your word for it. I would think even for a removable neck the block should be well adhered to the back as this provides much support.
Is it possible that it is simply undercut. I've thought of undercutting mine, but only by about a 1/16 or 1/32 gap and perhaps only 1/8" deep. I'd do this to hide glue squeeze-out. It's a pain to pick it out after it has dried. Tap on the back up near the heel....you should hear a tight tap sound vs and hollow sound where the block is adhered to the back. If you stick a feeler gage or something thin into the gap I suspect it stops just behind the leading edge, it is likely shallow. If not, then I apparently know nothing.