(weird it didn't get invalidated, tho... :/ )

Happy to report that Blind4Basics has fixed this issue. Consequently my code above no longer passes the test cases.

has the test-issue been resolved?

your solution catched my eye just by looking at the line-count :D

This solution is not valid, there is no checking for wrong ships placement.
Try
int[,] field = new int[10, 10]
{{1, 0, 0, 0, 0, 1, 1, 0, 0, 0},
{1, 0, 1, 0, 0, 0, 0, 0, 1, 0},
{1, 0, 1, 0, 1, 1, 1, 0, 1, 0},
{1, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 1, 0, 0, 0, 0, 0, 0, 1, 0},
{0, 0, 0, 0, 1, 1, 1, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 0, 1, 0},
{0, 0, 0, 1, 0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0}};

Should be false but your solution gives true.

Same problem.