bll0 on "strpos and header warning after upgrade"

Hi,
I just updated to the 1.4.4.3. After login, the already sometime mentioned error appears with

Warning: strpos() [function.strpos]: Empty delimiter in xxx/public_html/zp-core/functions.php on line 1515

Warning: Cannot modify header information - headers already sent by (output started at xxx/public_html/zp-core/functions.php:1515) in xxx/public_html/zp-core/functions.php on line 1614

Mod rewrite is on and working. If I reenter the url, the site appears completely correct.

I post this again as the solutions to others are not clear and/or do not match my configuration.

Thanks for your help!
Regards,
bllo