Bug introduced in V10.0.0 or earlier and persisting through V12.0
Let's create an example and do the test:
CreateDocument[{}, InputAliases -> {"[" ->
RowBox[{"\[LeftDoubleBracket]", "\[SelectionPlaceholder]", "\[RightDoubleBracket]"}]}]

As you can see this is not what I expected. SelectionPlacholder has changed to Placeholder.
OS: Win7
Can you reproduce the problem? It is not only the case of custom aliases but each built-in behaves the same...
"\[Placeholder]"both in v.8.0.4 and 10.0.0 under Win7 x64. But in v.8.0.4 the placeholder is selected while in v.10.0.0 it is not selected and when I type the text is inserted to the right of the placeholder. – Alexey Popkov Jul 24 '14 at 10:02\[SelectionPlaceholder]s generated by input aliases are no longer selected in v10 (Mac OS X 10.9.4) but, for example, if I create an indefinite integral "template" using the typesetting palette button (equivalent to theinttinput alias) the first placeholder is selected. – MikeLimaOscar Jul 24 '14 at 10:39InputAliases->{ "[" -> RowBox[{ "\[LeftDoubleBracket]", "\[SelectionPlaceholder]", "\[RightDoubleBracket]"}]}– Patrick Stevens Oct 18 '15 at 09:36