When trying to place a random blueprint over water (using Shift+Click) on Nauvis, it refuses to place the entities over water and doesn't place blueprint.

The behavior is the same regardless of the state of the landfill toggle button in the toolbar (gray or yellow background).

I have also noticed that when enabling the mod in an existing save, it "unresearches" the landfill research. Re-researching it does not fix the issue.

I'm on Factorio 2.0.77, using the mod version 1.0.2 Disabling the mod instantly fixes the issue.

Thank you for your report.
Not at game pc now, but could it be a conflict with another mod?

Tested again, but I cannot yet reproduce it. Would be helpful if you can provide more details.