Shot in the dark:
At the login screen, click the "session" button and choose icewm.
I saw the note saying do not do the following: but did it anyway:
Do not:, in gslapt, do update, mark all upgrades, install.
My symptoms were similar to yours, and included a switch to Nautilus. Selecting icewm session solved the problem, but didn't remove all those extra files. From then on, icewm will start because it's now your default session.
There may be other reasons this would happen. If you prefer Nautilus and installed it intentionally, that may have done it. Still select icewm session, then start Nautilus in ~/.icewm/startup. No idea what incompatibilites are there, but they can be solved. If you're going to use Nautilus, you'll need to comment out or remove pcmanfm in startup, like Nightflier suggested with your testscript.
The testscript idea's a really good one. If it runs as expected with no errors, chances are you're not using icewm now. If it has errors, post them if you need help.