Apparently the behavior of the earlier versions was found to be fairly useless (as the result is empty) so the R18 version now performs a virtual "make editable" before combining the polygon meshes. (I do not have any of these versions left installed, so this is theoretically speaking.)
Now, what do you want as the result, and what version are you in? If you want R14/15 to replicate the newer behavior, you could e.g. go through the selected objects and perform the "make editable" on a copy first, before executing the "connect objects" on the copies. If on the other hand you are in R18 and do not want this function to work on parametric objects, you'd need to go through the selected objects as well and refuse execution of "connect objects" if there is any parametric object found.