I'm not an expert on this nor did I got forum/wiki digging for more info yet. I'm just quickly posting my experience here.
I will say that, on my level 18 cleric atm, it seems like my casting skills are capped at 95 while my melee combat skills are capping at 90, so this seems to support the idea that casters have lower melee caps than melee, and possibly vice versa. And one could say that a plate wearing cleric is a little more designed for a bit of melee than a druid, hense maybe why my skills are only -5cap while yours is -10cap. But again, this is just speculation.
Another possible issue is, are you referring to the skill showing in your skills window, or the skill-up messages in your chat log?
I ask this because I also noticed an issue on my cleric that might be related or totally unrelated. I'll give the details and you can make the call on that. I'm using the default UI that comes with the Titanium client after the p1999 files are applied.
What's happened to me is (and this was present during my earlier levels as well), is that the number in my skills window and the chat message were not the same. For my 1h blunt (which is the only weapon skill I've worked up), it shows in red and as a lower number in my skills window, and often not as a multiple of 5 either. Like now at level 18, my combat log shows that I skilled-up to 90, while the skill window shows it in red as 76. I have no debuff or any other thing I can think of that would lower it (not overweight, tried taking off shield, etc).
I did some forum digging the other day about it, and while I didn't find a definitive answer, people seemed to think the red skill window number is just a display anomaly caused by the client for some reason, and that the number used in any actual combat calcs is that 90 skill that the combat log showed for me. I hope that is correct, but thus far I haven't been able to find anyone to say for sure.
Also, you can find info about the max level caps for class by skill here:
http://wiki.project1999.org/index.php/Skills