Update:
So... after trying to fix issues with textures in IC2-lf I switched to the experimental build (I've deleted most of the regions to regenerate the ore). So I'm fine with that, I had a quite new world. Thanks for this advice.
Problem is that my friends have large worlds and they kind of don't want to switch to the experimental version because of new lead ore and large industry chains. I've tried to fix that on my own, but I'd probably need some advice.
First of all: I know exactly which lines cause the issue and how to fix that. But I'm unable to compile the ic2-lf source with proper mcp/forge version.
Steps I tried:
1) decompiling the jar using jd 0.3.5
2) moving source to my mcp project
3) I got lot of errors with unknown method names (probably because of obfuscation) - again, I've used the same version of mcp/fml which are mentioned in the -lf build
Another scenario I've tried is editing the class file, but I got error when I'm trying to run minecraft with fml - it is unable to locate the edited class.
It is possible to get the abandoned -lf source wo obfuscation? It looks like it is abandoned considering the last build date, so I would like to fix it on my own. Or maybe I'm just doing sth wrong with the -source from the lf build. Anyone any ideas how to solve this problem?