git apply fails because of 'index xxxxxxx..yyyyyyy' line?

Hello

I was playing with 'git quiltimport' feature, trying to import a large quilt
patchset (coming from vendor) into a local git repository containing linux
kernel tree.

Some of quilt patches in the patchset have been created by picking single
git commits, likely with 'git show XXXXXX > file.patch.

And I found that such patches fail to apply with 'git apply' (which is
internally used by 'git quiltimport'). Git complains:

fatal: patch with only garbage at line 3

However, if I edit patch file and add a space before the
'index XXXXXXX..YYYYYYY' in the header, then patch applies cleanly!

Also, some patches did not apply with error message that looked like

error: removal patch leaves file contents
error: arch/arm/mm/mmu.c: patch does not apply

But these patches applied cleanly after I addeed a space before
'deleted file mode XXXXXX' lines.

Finally, some patches fauled to apply, with error message

fatal: patch with only garbage at line 3

but applied cleanly after I added a space before
'dissimilarity index XX%' line.

The mentioned addition of spaces do not modify patches themselves. But it
makes 'git apply' happy.

I'm confused.
Could someone please comment on this?
Isn't it a bug in 'git apply'?