I think i get a similar thing;

When i was up at innerliethen on the trusty hardtail after a couple of runs i started to get a feeling in my fingers, all of them.
It got progressively worse until i got to the point where i literally couldn't grip the bars anymore and the pain was unreal.

Once at the bottom, back at the car i attempted to take my hands of the bar and straighten my fingers, and honestly the pain was unreal and it took allot of effort to straighten my fingers.

Not sure ifs the same thing and i don't know what it was.

All i know is that i had unbearable pain in every joint causing me to not being able to grip the bar anymore.

But every day riding isn't a problem

Strange...

i have something similar i think, are you using 1 or 2 fingers to brake and what are the reach on your levers like?

I get this, usually only happens in my middle fingers though. Feels quite tender on the underside of my finger just before the first joint in my finger. Ive been back from france for 2 weeks now and i still have the pain. But to be honest it dosent effect my riding at all. I can live with it quite easily.

i get that pain, i know its not always possible but try gripping the bars less hard i find this helps when on a run

Read my first post, got some advice for it there. If you wanna try building up your forearms, only use minute weights (like 3 kg).
Remember it's lactic acid build up, so stretching and of course rest will help. Google "forearm stretches" or something, it's difficult to explain over a forum.

It's not arm pump!!! I know what arm pump is, and it definately doesn't still affect you hours after your ride.

True 'AMetalSlug'....they have had quite a battering! I'll give them a rest....when it rains.

I get this reaaaally badly.

What i've found helps is to get electrical tape and wrap it around the part of the finger that hurts, and also plenty of ibuprofen.