[Typo3] Hook "contentPostProc-all" in TSFE doesnt affect cached pages

[Christoph Singer]

Hi all,

I'm using Version 3.8.0
I want to modify the whole page content after generation of a page.
In class.tslib_fe.php I found the hook "contentPostProc-all" which is
described in the source code as "Hook for post-processing of page
content cached/non-cached".

I made a script with a function that hooks into this place. The function
modifies $GLOBALS['TSFE']->content.
When I clear the FE cache and view a page the first time, the hooked
function works: I see the modified page content.
But when I reload the page in the browser, the UNmodified content is shown.

Most strange thing: After viewing the page for the first time after
clearing the cache, I looked into the database an noticed that in
cache_pages the right MODIFIED page content is stored. But when I reload
the page, the unmodified content is shown and in cache_pages the
unmodified content is stored!

Can someone explain me whats going on?

It seems that
1. The hooked function correctly modifies $GLOBALS['TSFE']->content,
this correct modified content is shown (if the page is called the first
time) and the modified content is even saved in cache_pages.
2. When the page is viewed a second time, the unmodified content is
shown, even though in cache_pages there is the right modified content.
And then this unmodified content is saved in cache_pages. Where does
this unmodified content come from? Is it newly generated (bypassing the
hook), or is it cached in another place? Why I don't get the content
that is stored in cache_pages? Why the content in cache_pages gets
overwritten?

Am I doing something wrong, e.g. does my hook function need to modify
other things than just TSFE->content?

Thanks for any tips,
Christoph