Unexpected action when use with ultisnips

[tenfyzhong]

@SirVer I found some unexpected action when I expand a snippet. For example, I expand a main snippet, and use ycm to complete my function, after that, This plugin will expand the parameters of the function and select the first parameter. And then, I type <m-n>, this mapping key will jump to the next parameter, but it erase the selection word. If I remove the ultisnips, it work well. Can you give me some help what happen when the snippet expand? Thank you.
This is an unexpected example:

This is what I expect:

[tenfyzhong]

I have fix this bug by this statement.

let g:UltiSnipsMappingsToIgnore = get(g:, 'UltiSnipsMappingsToIgnore', []) + ["complete_parameter"]

But I don't why.