I upgraded to 2.8 recently and am getting PHP errors, while logged in as super-admin, whenever a cached page is updated (such as adding an entry or clearing caching.)
A PHP Error was encountered
Severity: Warning
Message: trim() expects parameter 1 to be string, array given
Filename: libraries/Functions.php
Line Number: 2456
A PHP Error was encountered
Severity: Warning
Message: trim() expects parameter 1 to be string, array given
Filename: libraries/Functions.php
Line Number: 2456
A PHP Error was encountered
Severity: Warning
Message: Cannot modify header information - headers already sent by (output started at /path/to/codeigniter/system/core/Exceptions.php:170)
Filename: core/Common.php
Line Number: 442