Ok, after further testing I was wrong, it wasn't a click length issue, sorry if you wasted time searching in that direction ops:

However, I found the real bug I had confused with a click issue :twisted:
Apparently the map isn't fully cleared up between games, making some squares unavailable for placing a tower. I can reproduce it here by starting a game, placing 3 towers in the 3 adjacent squares above the road



then hit "ESC", start another game and start placing the same three towers



and you won't be able to place the last tower.

At first, I hadn't noticed the color of the square changed (a bit dark and too much based on red-green for my eyes - yeah, I'm in the 10% of the population that is somewhat color blind )