[Plugin: Image Widget] PNG destroyed after Save

For my company websites, which you can find here (yes they’re very alike!)
http://www.alysgo.nl/contact/
http://www.inmote.nl/contact/
I have lists of logos in the sidebar. These lists have been here for a while. Now I’m asked to add TomTom to the list on the Alysgo site.
I’ve added the Image Widget, I upload the TomTom logo, fill out the settings. Then hit Save.
At Save, the little logo becomes a dark gray block with some jaggy edges on the right. Every single time I do this!
I’ve tried inserting and saving a different logo I already had in the same widget. All goes well.
I’ve tried using a new widget. Goes wrong again.
I’ve tried saving the file in Photoshop anew, upload, insert, different name, yada yada. All goes well until I have to Save the widget. It just turns the image into a dark gray jaggy bar.
I’ve just created a Samsung logo, and I get the same trouble. It looks like this is done by the Image Widget, because the Media Library handles everything fine.
Tried saving it as sRGB or not, Meta info or not. No difference.

Still I don’t get why the image gets destroyed. It isn’t saved anew? It’s just like it is in the Media Library! And there it is correct.