DBG5/DBG4 Grip

Can anyone tell me what Pentax were thinking with these grips.

I assumed the K3II took the DBG4, but SRS sent me a DBG5 which looks identical with the exception of a larger locating pin at one end. It obviously won't fit the K5.

Is there some fundamental difference with the inards/electronics?

I had a third party grip for K5 so I tried to put it on K3 when I got that. One of the locating pins was larger so i used grinder to remove it. I did mount on K3 to a fashion (wobbly as hell and not snugly fit ) but didn't work properly. I've seen post on pentaxforums.com showing someone making it work on K3 but not all buttons worked properly, so I think there are some differences apart from shape.

Greg