DD15 does some stuff like this - and it is with common words, not complicated ones that maybe you have seen in print but have not heard. I can't recall the words that are like the OP's example at the moment, but when she sees "Tear Here" on a package, she almost always says "tear" as in the crying pronunciation, not as in ripping.
She also did some weird stuff with mixing up opposites when she was younger. The most notable one was hot & cold - she didn't get that straightened out until she was 6 or 7. I put her hand on something frozen and said "cold" countless times, but she kept mixing this up. This was all part of the reason I thought the kid was "not college material" when she was younger. At one point, someone (a psychologist) told me what this issue might be, but she was past that stage by then and testing was expensive.
I wouldn't worry that much. My kid like this is clearly the best writer amongst my three kids and likely has the largest vocabulary of the three. It is kind of odd, but doesn't seem to get in the way of her academics or everyday life.
