There seems to be a bug with JPG compression. Automatic saving as well as saving from the editor correctly uses the quality setting from Options/Image File Format. But using "Safe Image As..." from the Prompt dialog saves the jpg with default quality.
There also seems to be no way to set JPG quality directly while saving. Help suggests a quality option in the file-save dialog but in version 4.12.0 that's nowhere to be found. There's only the image preview added to the file-select box. (I'm using Windows 7 x64 Ultimate)
And while we're at it, some suggestions:
The quality setting seems very coarse. With the capture I used for testing max quality at ~380kb is fine, the next lower setting at ~ 150kb already shows significant compression artifacts. Everything below that is completely useless. It seems the quality below 100% is worse than in every other program I know. Unless that's a bug, there should be more options between 100% and the next lower setting.
Also showing a percentage for the quality, like 100%, 90%, 80%, 75% would be helpful.
Other than that, great program!