Uploading a PDF also generates 4 JPG files

Looks like this plugin might have a compatibility issue with WordPress 4.9. Just after I upgraded to 4.9 MFM started to generate four extra files for each PDF I upload. It was working fine in 4.8 and 4.7.

These extra files are JPG copies of the PDF and are the three different sizes as defined in Settings/Media for Image files plus another presumably standard-sized one. It looks like WFM has somehow persuaded WP that PDFs are Image files. I deactivated WFM and an upload of a PDF worked without producing these extra file, so it’s definitely got something to do with this plugin.

Could be wrong about the explanation, but that’s what’s happening.

I realise the author seems to have abandoned this plugin, but is anybody else getting this? It’s an extremely useful tool for me and having set up quite an extensive folder structure in my Media Library I’m going to have to bite the bullet and just manually delete all these extra files every time I upload a PDF. Sometimes I do 10 at a time so that’s 40 files to delete. Or, deactivate it before and reactivate it after each time I do an upload. Unhappy bunny here but I suppose this is the sort of thing you have to expect from unsupported plugins.

Has any code-shark out there got time to dig into this ane find a way to avoid this symptom?