Leading numbers in template variables leads to blank page / zero output

A leading number in template variables - e.g

leads to a blank page.
This could be easily tested by replacing

in index_body.html to

. Or any other variable, as long as a number is leading.
In phpBB 3.0 the result is, that the current time is not displayed anymore (as the variable is not defined), but the forum index is shown.
In phpBB 3.1 the result is a blank page, the output dies.
This is just an example, also defined variables with leading numbers are leading to a blank page.