I've stopped using Spectro on the account of it not being able to utilize my resolution of 1440p- it is just to small on my screen
I've seen such data many times and was suspecting what you just described- a lossy mastering
One symptomatically case [and the final proof to my thesis] was that of music from the 1982 movie "Blade Runner", released as late as in 1994. Wanting to upgrade it from some old MP3s I downloaded one set of FLACs- and they were stopping at ~20+ kHz. So I search for another source- there were the same. So I went to my closet, took out the box with CDs, ripped the original disc [EastWest Records America 4509-96574-2] with Audiograbber on maxed out settings and there it was- a blank space above 20 kHz. Here is an example, the song "One More Kiss, Dear":
And just to make sure I checked the 2007 Special Edition of that score, which on disc 3 contains additional music [not the original compositions]. Here is the track "Up And Running", which samples heavily that "One More Kiss, Dear" song:
It is quite masked with all the new sounds with which the layered the sampled original, but for me to spot such a cut off line is no longer a problem- if I see something like that then I suspect that something like a lossy samples are the culprit. And also comparing different tracks from the same album can tell a lot. That is most evident with OSTs, were you have music from different sources
As for Fakin' The Funk. Here are spectrograms made by it for those same file of "One More Kiss, Dear" and "Up And Running"
For sure I would never spot the issues of samples in the "Up And Running" as I did in Spek. And the "One More Kiss, Dear" was reported on the list of files as a positive [green thumb up]- and I checked the settings [aggressive, report above 256, analyze entire]. So it seems that although FTF has easy interface and can be used for mass check-up, the results may be incorrect