Somewhere between beta3 and rc1 the ability to put exposed forms into their own block's disappeared for content panes.
1) Install clean site, enable Views and Content panes
2) Create a new page display. Note the option "Exposed form in block" being available.
3) Create a new pane (or context) display. Note the same option now missing.
I tried with both stable and -dev of ctools aswell.
Assigning directly to dereine as I can't figure it out and it's a D7 issue.
If I can figure git-bisect out I'll pin-point the commit later.