@Zukny - Thats probably a bad idea; you don't want strangers messing with your content. Ive read some places that they used the role manager plugin to repair this bug by changing the level of the subscriber user.
Im not entirely sure why this bug happens (it does not affect everyone), you could check the user's level is shown by wordpress by doing the following. This is the check the plugin does to see if your logged in:
if ($user_ID != '') {
maybe you could see if it outputs a user level at all when your a subscriber? You could check by putting the following code above that line in the plugin (line 107):
echo 'The user ID is '.$user_ID.'.';
That may reveal the problem - please post your results.