I'll lead this post by admitting this is probably windows' fault and not Netbeans nor WinSCP's

OS: Win 7
WinSCP 5.13
Netbeans 8.2

When using right click > File > Open on remote files, Netbeans stalls for a seemingly random amount of time (a couple of seconds up to a couple of minutes) until it finishes loading. The new file tab opens almost immediately but it is empty and no other action will register whiile Netbeans is in that state. It is apparently waiting for the file to load.
This is likely due to some race issue on the file being extant and available in the filesystem.
I have observed this behaviour before in previous versions of windows and other FTP clients and other IDEs/text editors, which makes me think this is likely a Windows issue.
Also likely to be an issue with an AV locking down the file immediately after it is created to scan it.

Potential workaround: after putting the temp file in the filesystem, check if it is available to open, if not, wait and retry xxxms later. Launch/Open the file only after the resource is free.

Problem: Figure out what 'file is available' actually means in windows.

:)