I think it's funny when my fiancee says words that end in "A" he puts in an "R" and vice versa if the word ends with an "R" he puts in an "AH" (I think that's what it sounds like anyways!)...So for example, instead of "PandA BeaR" he will say "PandER BeAH" or like "Tarantular" instead of "Tarantula"...His friends do that to!
I'd say that's a mixture of the local accent and also the way a lot of us Brits pronounce the 'a' at the end of a word (from the way you've described how he pronounces those words, I'm guessing your fiance is from the West Midlands area?).
We usually don't consciously 'put an r at the end', but actually we just end the word with an 'UH' sound for the 'a' so maybe it sounds like an 'r' to others, especially if it's then followed by another word (i.e. panda bear). In terms of the 'AH', US accents tend to have a harder 'r' sound whereas UK accents have a softer 'r', which can sound like 'ah'. I also say it kind of like 'pand-uh beah' - that's just my accent. I grew up in the West Country, but I don't really have a West Country accent... if I did though, I would probably say both words with a strong 'r' at the end: 'pand-err behhrr'.
And it STILL drives me CRAZY when they end EVERY sentence with a question!!
Me: Honey, what is the weather supposed to be like today?
Him: Oh, it's supposed to be cold with rain isn't it?
(I typically respond back "I don't know, IS IT?? That's why I asked you!")
Conversely, though, you can get a similar thing with some American accents... where people seem to end every sentence with a question (i.e. the typical 'bubbly teenage girl' who lifts her voice at the end of every sentence so it sounds she's asking a whole bunch of questions. And don't even get me started on phrases like, 'I know, right?'

(why are you asking me whether you know or not?

)). It's not just UK accents that have these kinds of quirks.