wow have never had that. I think.
I had a crazy one with ICH9 raid the last few nights but...
If you go back from the partitioning step (to step 3) and forward to it again it resets the partitioning. also resets if you go back to partitioning from a later step.
I would not use delete unless you really want to delete the partition.
removing the mount point entry for the partition stops it being put in the fstab.
if you dont want to use all your swaps you have to set their fs type to nofs (or something like that. last option in list).
if you are going to use hdb7 you could try deleting it and making it new since it is going to be formatted anyway. hopefully this will get rid of your size problem.
the other thing to try is to use gparted from the administration menu to check what it thinks the disk layout is before starting the install.
but i have found the installer partition editors to be better/see more.