I have seen it where you shoot an enemy head on and get the shield marker, but I believe the shot simply went high a bit and hit the shield.
And I also agree they need to be removed. It's just the next piece of cancerous equipment in this game beeing annoying after S mines saboteur and fireshotguns unlimited grenades etc. But I just like gunplay so that's just me.
If you want to know how to exploit it. Equip a shotgun as secondary. Defend against the attacker and blast him as he reloads. Or if you are on a bit of lag, simply swap to shotgun when you're close enough and the attacker has no way to respond fast enough, especially if he lags a bit himself.
What works for me against shield users though (lag works in both ways) is circling them. If you lag a bit their playmodel doesn't update fast enough and you can shoot them in the side as they appear to be facing another direction. Even though on their screen they had you in de window at all times.
I get that shield hitmarker all the time but I put it down to bad hit detection and forgot about it.
The counters for shields are almost endless btw guys but my favourite would either be satchel charges for maximum effectiveness or the jumping shotgun blast to the top of the head works too, most of the other countermeasures have been posted in here or in similar threads.
Cavalry, saboteur and satchel charges is great for killing those pesky campers and if you use the mp40 or combat shotgun secondary this class becomes quite OP imo.
Stickies, launchers, flamethrowers and incendiary bullets need to be removed because they can all blow the living colours of the rainbow out of me and my amazing shield...Little tip for ya right there.