Suggested resolution:

Change in 8.5.2 [stmt.if] paragraph 1 as follows:

... In the second form of if statement (the one including else), if the first substatement is also an if statement then that inner if statement shall contain an else part A selection-statement is never interpreted as an if statement having two substatements if the first such substatement would be an if statement having only one substatement. [Footnote: ... ]

(From submission #947.)

The last sentence in 8.5.2 [stmt.if] paragraph 1 is phrased as a semantic constraint, but is intended as a grammatical disambiguation rule:

... In the second form of if statement (the one including else), if the first substatement is also an if statement then that inner if statement shall contain an else part. [Footnote: ... ]