APM login fails if HTTP request chunking is enabled

Dear all, I'm trying to modify the content of a submitted web form (HTTP POST request) using an iRule and a STREAM::expression + STREAM profile. This only works properly, if I set the "Request Chunking" parameter to "Rechunk" in the corresponding HTTP profile. But in this case APM logon doesn't work any more. The problem seems to be related to the APM internal "/my.policy" page, which doesn't process the submitted login form correctly. If I change "Request Chunking" back to "Preserve", APM logon works fine immediately.

 

Has anyone seen this strange behavior before? Please let me know!

 

Many thanks and best regards, Oliver