Windows don't knows .sld files

[Thunichgud]

I just installed XnViewMP 1.3.1 on Windows 7.
After that I created a slide show inside of XnViewMP. The file extension is .sld.
After closing of XnViewMP I tried to start the slide show by double clicking onto the .sld file. Windows could not start the slide show because it didn't know the file of this type. I had to select in the following dialog the belonging program. I also activated the option to remember this program for this file type.
After that, the slide show started, but after closing XnViewMP and again clicking on the .sld file Windows didn't know this file type again.
I looked into HKEY_CLASSES_ROOT of the registry, but there is no .sld or XnViewMP.sld registered. There is a XnViewMP.slide registered but renaming my .sld file to .slide had no effect.
I installed XnViewMP two times with the setup but this did change nothing.

Is it a bug, or what can I do to solve this problem ?

[xnview]

you can associate .sld with XnView MP to open them