ARM-ELF -> PE-COFF with objcopy

[i-love-spam]

I tried some stuff and I noticed that if I pack and unpack .dll with upx they aren't identical anymore.
if I try to:
arm-mingw32ce-strip.exe -s mydll.dll

and then if I try to use upx I get this error in red color:
upx: mydll.dll: InternalError: FIXME: soxrelocs != assumed_soxrelocs

I downloaded upx src and there is no such code with this error message! Any ideas what could be wrong? Is that strip corrupts the dll?

By the way, strip -s means "Remove all symbol and relocation information", what kind of impact does it have on the final release binary is it ok to do it or better not to?

Thanks