Yes that can happen. You can wait a moment and then wiggle over the spot where you got the tone change and should get a correct id. You have to work the signal. Also,as far as fast/slow response goes, a lot depends on your settings (filters being used) and amount of disc you are using. ETrac can be set to be a bit faster. I am guessing you are using Conductive Multi tones. Also coil size will help for a faster response in target rich areas.
What kind of areas are you hunting???Parks,school yards.
I find myself using Ferrous with 4 tones. But I hunt old town lots loaded with any kind of metal you can think of, also old long gone plantation sites. Ive mostly used the Sunray 8 inch coil in these areas until recently, I purchase a 4.5x7 excellerator coil (eliptical with a closed design). This new coil has really opened some of these old spots making hunting in the trash much more manageble,not in the fast response area, as say a F75, but pretty darn good with not a lot of depth loss. Ive found coins at 8 inches in the short time Ive had it. I dont think its coming off my machine very much.
But, when I park hunt,or hunt a place where I dont wanna dig very many holes and have to be more selectable, I will change my tactics. Conductive Multi tones,more disc will be used.
Hope this helped and Im sure others will have their takes and experience,
John
ps,edit
Johnnyanglo has an excellent post on the audio with graphs,,,read that very educational