Yes, I think that's the best hypothesis at this point.I've got a series of captures showing "real" EH on a day when its frequency is fairly steady, then gradually a "ghost" EH fades in a Hz or two lower in frequency. The usual course of events is that this state of affairs persists for several minutes, then the secondary trace gradually works its way up in frequency and either fades out or merges with the original. On the day in question, though, the receding path became the stronger one and the primary path faded out completely for several minutes; after which, the main path gradually returned and the receding one faded. If you look at the captures from a distance, it looks just as if EH dipped in frequency by about 1.5 Hz and then returned. It's only if you look closely enough to see the two traces coexisting that you realize one temporarily replaced the other.
What's odd to me is that I've been listening and watching from my farm for three years now, and the effect never showed up at all during the first two years. About a year ago, it happened once on the EH signal. Some months later, it began happening on an intermittent basis. Now it's almost a daily occurence in the late afternoons, and also happens to other signals at times.
This January, after witnessing the effect on three HiFERs in the same afternoon, I stumbled across the KL7L 30 meter grabber in Alaska and saw the effect was also quite common on that band at the same time.
Perhaps there is some phenomenon unique to Solar Max or the downslope therefrom that has gone unnoticed in the past, before so many people were watching signals with spectrum analysis?
John