A common scientific term to describe what you are talking about is called negative transfer. I.e., where learning one skill actually results in lower performance on another skill. This is contrasted with positive transfer, when learning one skill facilitates performance on another skill. In general (although I don't have refs on hands) positive transfer is generally a greater effect than negative transfer. Negative transfer tends to be localised to particular aspects of the task (e.g., b's and d's).
For a extended encyclopedia entry see Perkins and Salomon's (1992) article on transfer of learning.
Research on Mirror Reading and Writing
There's even research specifically on reading and writing upside down and back to front (e.g., see google scholarfor 'mirror writing' and 'mirror reading'). I haven't read much of this literature.
To take but one article, Gottfried, Sancar, and Chatterjee (2003) discuss acquired mirror writing.
They note, perhaps relevant to your question, that:
Young children, developmental dyslexics, and some healthy left-handed
adults may produce mirror text.
I assume that in the above cases (as opposed to your case where it is acquired with deliberate practice), writing in reverse is involuntary, in which case I suppose you could describe writing a few letters back to front involuntarily as representing a symptom shared with some developmental dyslexics.
As an interesting historical aside, they note that
Perhaps the most celebrated mirror writer, Leonardo da Vinci,
generated over 5000 notebook pages in reverse.
So, you're in good company.
- Gottfried, J., Sancar, F., and Chatterjee, A. (2003). Acquired mirror
writing and reading: evidence for reflected graphemic representations.
Neuropsychologia, 41(1):96-107. FREE PDF
- Perkins, D. and Salomon, G. (1992). Transfer of learning. International
encyclopedia of education. FREE LINK