E_STRICT warning in cache_get()

I ran into the following php error after the update from 1.8 to 1.9
[type] => 2048
[message] => Only variables should be passed by reference
[file] => /home/tcnetwork/public_html/sites/all/modules/memcache/memcache.inc
[line] => 319

I found out it seems to be due to a combination of php functions stringed together. As soon as you break them up the error dissappears. Fixed it by doing this:

$tmp = array_keys($wildcard_flushes[$table]);
$wildcard_length = strlen(reset($tmp));

php version 5.2.13-0.dotdeb.1