In gvim using netrw(the file explorer), I usually middle click a file to open it in the last active window. This just leads to an error stating "Cannot make changes, 'modifiable' is off". Another middle click, and the file opens fine where I expect it to. All buffers are saved, there's no uncommuted changes anywhere.
What causes this, and what can I do about it?
Here's a picture of when I middle click a file: