UV "protection" filters are not too unlike putting plastic runners over your carpet or slip-covers over your furniture. In theory they "protect" against something, but who or what are you saving it for?
 
The sunspot flare that you are experiencing is highly likely being exasperated by the filters. One of the easiest tricks in the book for improving your photography is usually just removing the "protective filter" and keeping the glass clean.
 
Nowadays, we have the iPhone, iPod Touch and iPad. You can buy these "protective" films (as advertised on this very site) to go over the glass. Again, why?  Why put up with the additional surface to look through, the ugly look, the reduced effectiveness and accuracy of the touch-screen?  To protect it from SCRATCHES?  It's awefully hard to scratch this new glass used in these devices. If you are going to scratch it, chances are you're going to break it first.
 
But we do these things to "preserve value". Ooooooooookay. Again, for what/whom are you doing that?  Unless trashed, most used lenses are pretty much about the same price regardless of whether you used a protective filter on it or not. As to cell-phones and other consumer electronics, they have no value, used, anyway. The moment a new model comes out, your existing one is nearly worthless.
 
UV "protective" filters serve a purpose if:
1. You're photographing around water,
2. You're photographing an industrial site with abrasive and oily materials in the air,
3. You can't help yourself from sticking your fingers on the glass all the time,
4. You smoke and the haze builds up on your equipment,
5. You're photogaphing at high-altitude and need a UV filter,
6. You don't use lens caps,
7. You photograph motorsports from the fence opening on the outside of a turn.
 
I'm sure there are random other examples, but you get the idea.
 
Think about it this way--the average non-professional hobbiest photographer keeps his camera safely tucked away inside a camera bag until a picture reveals itself. Only then does he/her remove camera from bag, remove lens-cap from lens, shoot picture and then put lens-cap back on the lens and the camera back in the bag. It is not unusual at all for a five-year old lens to have been exposed to the air for less than two hours total.  Personally, I can get two hours of air-time on my lenses before breakfast!
 
Another thing about UV filters which most people don't realize. Due to the disparate materials and the plastics used in the filters and lenses, it is very common for the filter to become statically charged which attracts dust, oils and other gookies in the air directly to the filter. It never ceases to amaze me how quickly my filters become hazy. (I use filters for B&W photography and polarizers). The bare lenses rarely become hazy, but the filters will get so with only an hour of exposure.