Strange collection errors occuring on only some workstations (apex 2.2.1)

Question

Hi there,
Firstly I have to say this excellent forum has been my primary educational tool for Apex. I have been here everyday for a month and this is the first time I felt the search button has not provided me with the solution I am looking for!
I have two questions, probably related:
1.) Why is it that collections are not session dependent? For instance if I run a new instance of my application (with a 'clear cache for current application' process running on a new instance), all my session variables, application items and collections are empty (as they should be). BUT if I run the application and create a collection, then start a new instance of the application SOMETHING GOES BAD. Checking the session variables I can see that all application items and session variables are empty - but the
old collection has not been deleted!
I even tried a process like this (runs on new instance of applciation before computations and validations):
So collections are not dependent on a session? Why not? How can I be sure to clear a collection everytime a new instance is started?
code for 'clear cache for current application':
begin
IF APEX_COLLECTION.COLLECTION_EXISTS('FILTERED_HOLEID') THEN
APEX_COLLECTION.DELETE_COLLECTION('FILTERED_HOLEID');
END IF;
end;

Answer 1

Thanks for your response.
Not a true statement. Collections are only visible within the APEX session where they were created. When you try your test, are you sure you're using a truly distinct APEX session identifier?
Perhaps I am missing something, here are my steps:
1.) Open url of application: http://server:7780/pls/apex/f?p=100
2.) Apex automatically redirects to a new session: http://server:7780/pls/apex/f?p=100:1:732674747920700151
3.) Run application and open session information at bottom of page. Collection is as expected.
4.) Open NEW page of application: http://server:7780/pls/apex/f?p=100
5.) Apex automatically redirects to a new session: http://server:7780/pls/apex/f?p=100:1:4699901634435334125
6.) Open session information at bottom of page. Session ID is different (as can be seen in url) however THE ORIGINAL COLLECTION still exists. All other session items are blank or null as expected.
Are these numbers not truly distinct APEX session identifiers? Is the fact that I am using no authentication having some kind of impact?