Einsteinians teach that, for all kinds of waves (light waves included), the wavefronts bunch up (the wavelength decreases) in front of a wave source which starts moving towards the observer:

https://www.youtube.com/watch?v=h4OnBYrbCjY
"The Doppler Effect: what does motion do to waves?"

http://www.amazon.com/Brief-History-.../dp/0553380168
Stephen Hawking, "A Brief History of Time", Chapter 3: "Now imagine a source of light at a constant distance from us, such as a star, emitting waves of light at a constant wavelength. Obviously the wavelength of the waves we receive will be the same as the wavelength at which they are emitted (the gravitational field of the galaxy will not be large enough to have a significant effect). Suppose now that the source starts moving toward us. When the source emits the next wave crest it will be nearer to us, so the distance between wave crests will be smaller than when the star was stationary."

For waves other than light waves the moving source does indeed emit shorter wavelength - it is the same for all observers, including one moving with the source. That is, all observers measure the wavelength to be L when the source is stationary, and then all of them measure the wavelength to be L' (LL') when the source is moving.

For light waves this is obviously not the case. For instance, an observer moving with the source measures the wavelength to be L, not L', which simply means that the wavefronts do not bunch up in front of the moving source.

Conclusion: The moving light source does not emit shorter wavelength - rather, it emits faster light. If the source starts moving towards the observer with speed v, the speed of the light relative to the observer shifts from c to c'=c+v, in violation of Einstein's relativity.

Pentcho Valev