Default save extension is "Normal Text" but Notepad++ is saving without an extension

New style save dialog has to be set to disabled for file extension suffix to work.

1. Menu » Settings » Preferences
2. "Default Directory" tab
3. Uncheck "Use new style save dialog (without file extension feature)"

I found an answer that fixed this for me (versions 7.3.2, 7.3.3. and 7.4.2)

Settings->Preferences->Default Directory->uncheck Use new style save dialog…

(Source) Posted by (Claudia Frank)