Well maybe burnt was the wrong word , they get FLAT or taste bad , I use TV Tobacco juice and it seems to gunk up things faster than other juices.
So it's not just me that has this problem, I have tried tastyvapors tobacco flavor and it's good BUT it clogs up my cartos super fast. I just ordered 2x48mg, 2x36mg, and 1x4ounce doubler of my peach-menthol flavor from tastyvapor, this is the only flavor that iv seen taste the same from day one to day 60, not like other ones that start tasting different after a few hours. Also the menthol adds a little TH to the vapor so you can lower the nic mg of the juice, I vape 24mg-18mg at night, the only reason I haven't lowered it is cause I'll vape more. I go through about 1ml a day and only take about two hits every 30mins. Now I just add a little of the tobacco flavor to my mix when I want a nice mellow tobacco flavor.
** note I hated menthol before I started gaping, but now I like it for the cool feeling and the menthol seems to add a nice TH to the vapor, also helping to lower both your voltage and your nic mg.