output_page does not show page

[Ad Bakker]

I am trying to help another member with an extension involving both forumdisplay and showthread. After some problems the forumdisplay part works, but now when a threadlink is clicked, showthread only shows a blank page (the correct url is shown in the address bar).

When I add some debug output to showthread, it appears that the whole script up to and including the call to and return from the script output_page at the end, is executed. This means that the echo at the end of output_page does not produce any output (also checked that this is executed).

I hope that MyBB programming cracks will recognize this behaviour!!


EDIT
I just see that when I add an echo just before output_page is called in showthread, the output of this echo is shown on the blank page.

EDIT 2
I now see that the complete contents of the page ($showthread) is empty.

EDIT 3
The only reason that I can think of, why the showthread template does not produce output, is that there are special forumdisplay and showthread templates used through XThreads.
I had first a similar problem with forumdisplay but that was solved by an unclear reason.

EDIT 4
I have dumped the template forumdisplay just before the eval statement in showthread, and this is the correct (XThreads version of this) template.
Question is now, how come that the eval produces blank output?

EDIT 5
All of the sudden the output of eval ($showthread) was the complete html of the page. However, it was not echoed by output_page. After rechecking, this only occurred once, and when I run the identical script again, the output of eval is again blank.