$START DATABASE blocks pclose calls ??

Hello, maybe you have an idea for the following strange problem. I'm maintaining an application written with C and ESQL/C. We're using a very old 2.1 Version of the Developement system (but it works) on PC hardware with SVR4 Unix.Everything works well. This application has to be installed on a customers machine (a RM 400 with Sinix V5.4.2 and Informix 4.1 Release). Because we hadn't this hardware in our company i had to recompile the sources there. No problems and nearly everything works. What's making problems: There is a part of code which accepts a system command, opens a pipe with popen with this command, read the output, close the pipe (with pclose) and returns the output. This code works until the $START DATABASE command in the code. Immediately after this command, the pclose call goes into blocking state. Maybe someone here has an idea what's going on and can give me a workaround for the problem. Greetings, Joerg