Lazarus, in the nature of things, closely manages all .lpr, .pas, .pp, .lfm, .inc files and the like in the current project. This is required for the tight integration between the Designer, Object Inspector and Editor.It is not unreasonable for the IDE to assume that when you want a new file you will use File->New unit or File->New form (or File->New...) so that the IDE itself initiates creation of the new file, and is not just presented with an operating system novelty that you have forced into existence by some back door approach.
Windows 10 64-bit, NTFS partition, Lazarus 1.8.0.Steps to reproduce:1. Have a project open in Lazarus.2. Manually create (via the OS, not Lazarus) a new .pas file. May need to be inside the project folder or at least a subfolder thereof, not sure. Your OS must be configured to open pas files in Lazarus. (I would assume this still happens with other extensions too.)3. Double-click this file, to open it in Lazarus.4. Lazarus will claim that the file does not exist when trying to open it and ask if you'd like to create it.5. If you say "No", then try to open it a second time, it opens properly.