It would have taken me much less time digging around in po code if you would have submitted a proper minimal bug report.
I have provided you with simple functions showing how streaming pages are supposed to work, using these should be quite straightforward for an experienced developer.
The function "ns_startcontent" was deprecated in NaviServer about 9 years ago, so i am not impressed by the the 7 years your code worked for aolserver :). The function was probably at no time working in NaviServer exactly as in aolserver (my guess is that the differences might be related with the various strange charset options in aolserver which are gone in NaviServer). It would have been probably better to remove the function in NaviServer 10 years ago, so the difference would have popped up sooner.
Anyhow, the right way for OpenACS applications is to use the abstractions provided by OpenACS and not using the low-level functions. These were introduced 15 years ago not without reason.
all the best
-g
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