When I try and convert the 12mb _merged.lsf file in the RootTemplates folder (of shared), it takes likes 40 minutes and converts it into a 500mb .lsx file which basically has same chunk of text with some minor variations repeated several million times..
It was an LSF parsing bug, fixed in v1.7.2 and again v1.7.3. In v1.7.3+ .lsf files should be converted to XML properly.