TMJOIN, TMRESUME and ifx XA lib

Hi ! Has anybody experienced how to use the ifx thxa multithreading-capable XA library and correctly create the associations for another thread in the same transaction ? We suppose to use xa_start with TMJOIN but it would not work. Also xa_start with TMNOFLAGS will result in errors when called in another thread but with the same rmid. The informix docs are not very detailed and the XA spec is somewhat sloppy talking about processes with regard to tx associations.. Any help is very much appreciated. --Chris