Is there a way to request this to be re-opened? The resolution to the issue this is marked as a duplicate of does not apply to the situation I'm describing. The other issue was marked as "Invalid" apparently because it was believed that the person reporting the issue just put water in the glass pane, which isn't what I did. Placing water outside the glass panes surrounding (not in the same space as!) the corner causes the inside to become flooded (or vice versa, as technically shown), which is extremely poor and irritating behavior.
All right, first I heard of it being intended behavior instead of being told I put water on the block. I feel like it should. not do that but whatever I'll use different corners then.