The template for viewing custom data from Contact >> View >> <custom group tab> winds up showing both the "show" blocks and "hide" blocks because the template (templates/CRM/Contact/Page/View/CustomData.tpl) invokes the function on_load_init_blocks() which is defined in Common.js - BUT that file is not available to any of the child contentPanes.
To recreate using sample data - modify the Setting for the sample "Constituent Info" custom data group so that Display is "Tab" instead of inline. Then browse to a contact record and hit that tab. You'll see both the show and hide div's (regardless of how "Collapse on Initial Display" is set.
I tried to fix this by adding a line in the tpl to include Common.js. That works for the "snippet" view, but not in the tab - so I'm not sure how to get Common.js included in a contentPane scenario??