different pdu.len for (HTTP) media/* dissector?

[varname <varname () gmail com>]

While figuring out how to access http bodies fom http responses, I 
noticed something about the reported lengths of pdu's in Lua. Using the 
following code:

____________________________________________________________

http_extractor_f = Field.new("http")
function tap.packet(pinfo, tvb, userdata)
   local http_pdu = http_extractor_f()
   print("pdu.len: " .. tostring(http_pdu.len))
end
____________________________________________________________


with a tap filtering on http packets I see this:

  - whenever a (reassembled) http packet contains a content_type of 
'audio/mpeg' the pdu length seems to be equal to: length(http header) + 
length(http_body).

  - for other mime-types (or at least text/html, image/gif and 
image/jpeg) this does not seem to occur. The http_pdu.len then seems to 
be equal to the actual length.


Is this expected behaviour, or is my code incorrect / wrong?

Example output (of a somewhat extended script):

____________________________________________________________

pkt.number      : 43
pdu.len         : 630
content_length  : 184
content_type    : text/html; charset=utf-8
body            : yes
media           : no

pkt.number      : 3557
pdu.len         : 3186271
content_length  : 3185898
content_type    : audio/mpeg
body            : no
media           : yes

pkt.number      : 12717
pdu.len         : 314
content_length  : 35
content_type    : image/gif
body            : no
media           : no
____________________________________________________________

regards
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