Hello, i solved my problem maybe 2 weeks ago, until the official fix comes please perform these actions:
edit wp-config.php and add change lines:
define( 'WP_TEMP_DIR', ABSPATH . 'wp-content/tmp/');
also please create tmp folder inside wp-content folder and chmod it to 777
*you should chmod wp-content also to 775 or something liek this if it wont work maybe even to 777
Also bitnami has huge amount of problems when it comes to permissions but i'm afraid if i will lsit the problems nobody never will fix them and i have my own "hotfixes" to all the small problems to default bitnami.