Debugging help - PHP include causes page refresh -

i'm having odd problem can't seem track down. regards debugging greatly appreciated!

let me describe using scenarios.

scenario 1 (incorrect)

1. php calls out cas server (using curl_exec) , gets user info back
2. php checks database ensure user returned cas exists , fails (which correct, i'm testing non-existent user) , sets error message "user not found" (this correct error message)
3. php includes top.php file
4. the page randomly refreshes or redirects , starts process over...this can't figure out.
5. php calls out cas server (using curl_exec) , receives error since cas ticket has been used, setting new error message of "cas rejected credentials" (which not correct)
6. php includes top.php file , doesn't refresh/redirect second time
7. php prints out "cas rejected credentials" (which not correct)

scenario 2 (semi-correct)

1. php calls out cas server (using curl_exec) , gets user info back
2. php checks database ensure user returned cas exists , fails (again, correct, i'm still testing non-existent user) , sets error message "user not found" (this correct error message)
3. i skip top.php since commented out, , print out "user not found" (this correct error message)

debugging

so, have checked, double-checked , triple-checked top.php doesn't use include, require, redirect (a function wrote prints <meta> redirect tag , calls exit;), or other thing refreshes page.

in fact, i've put in die statement prints out error message. on 1 line in top.php, prints out correctly. when move statement down 1 line (below html </div> tag), refreshes page , prints incorrect error message. there aren't php tags anywhere close.

as far can tell, means problem not in top.php file, since printing out </div> should never cause page refresh/redirect.

any ideas on how debug here enormously helpful. clearing caches/buffers? how better track php doing?

note: no php errors being output.

update: yay, found culprit! instead of calling include 'top.php'; copied/pasted code inside login.php , presented same problem. began deleting lines until found 1 causing problem:

<meta http-equiv="content-type" content="text/html; charset=utf-8" /> 

so, switching question entirely since didn't have of question in first place: can explain why causes page refresh, , why (i.e. doesn't continually refresh page)?

if have firefox grab copy of livehttpheaders. turn on , go through scenario 1. trace through http request , response headers see happening there. should provide more information on happening between browser , server.