Ignore doesn't work as expected with nested subdirectories

[harto]

Hello, thanks for the great tool.

I'm seeing some behaviour re. .ignore that doesn't match what I expected.

Here is a repro:

mkdir -p /tmp/rgtest/a/b/c
cd /tmp/rgtest
echo hello >included.txt
echo hello >a/b/c/excluded.txt
echo "a/b/c" >.ignore

rg hello      # prints only included.txt (expected)
rg hello a    # prints only excluded.txt (unexpected)
rg hello a/b  # prints nothing (expected)

Can you help me understand this behaviour? I expected rg hello a to print nothing.