There is only one Maple syntax indeed. Essentially, whatever you write using that syntax when the display is 1D, you can write when the display is 2D with the same meaning. But then there is also (as the 15th order term in a series expansion ...) a very small number of things that change, mostly related to not leaving a space between operators, as for example the one you mention. However, you see: with so many years using Maple, programming in Maple, and having used 1D display of input as well as 2D display of input, I never - ever - crossed with this example you are mentioning now, simply put: wasn't even aware of it. If something, your example basically makes my point, in my opinion.
With all due respect, honest respect I have for you, vv, to think otherwise, that because of this example, then what you write when using 1D display doesn't work when using 2D display seems to me a blatant misrepresentation of the actual situation. People need to understand how this works 99.999 % of the time. It may even be useful to collect the minuscule exceptions, but not useful to think they are the issue here.
Most of the confusion about this, in fact, I think, derives from the mistake of calling these modes "1D input" and "2D input" when in reality they mean "1D display" and "2D display" of the same sequence of characters being input. Plus the fact that when using "2D display" of the input, you can, additionally, optionally, also use a space to represent multiplication, as we do with paper and pencil.
One last comment for Janhardo: what I meant by Maple syntax is not about programming. Maple syntax is just how we express mathematics on the worksheet. So 1+1 is Maple syntax, f(x), diff(f(x), x), all that is Maple syntax.
Edgardo S. Cheb-Terrab
Physics, Differential Equations and Mathematical Functions, Maplesoft