I dont really know how i can explain this

for weeks now, oil behaves weird.

when i place a pump right on a spring, it start pumping oil as usual, but when the spring part above the world is removed and it goes below sea level the pump is "digging" a hole in the oil field.

all surrounding oil is ignored

http://imageshack.us/photo/my-images/203/vsoo.png/
http://imageshack.us/photo/my-images/203/ojh0.png/

is this some kind of new behavior, or does this come from another mod? eg. Greg Tech?

mc 1.5.2
buildcraft-A-3.7.2.jar
gregtech 3.11a (i think)
lots of other

okay, but i cant believe something in 1.6 fixes it, because it wasn't there some weeks ago!

Come back in 1.6 if you still have issues.

I can guarantee one thing: it's not GT. He doesn't touch BC internals and it worked fine for me with those versions you listed.

Well all that code (yes ALL of it: pump code, oil code, etc...) has been rewritten for 1.6. So there is little chance its still an issue.