Tabs magically converted to two spaces when rebasing

Question

When I'm rebasing my branch, I get a merge-conflict even though I both sources has tab-indented content (for my project.pbxproj in Xcode).

Ok, so, I'm here:

$ git st
rebase in progress; onto b54f22f
You are currently rebasing branch 'feature' on 'b54f22f'.

What I rebase onto:

$ git show master:MyProject.xcodeproj/project.pbxproj | head -n 5 | xxd
00000000: 2f2f 2021 242a 5554 4638 2a24 210a 7b0a  // !$*UTF8*$!.{.
00000010: 0961 7263 6869 7665 5665 7273 696f 6e20  .archiveVersion 
00000020: 3d20 313b 0a09 636c 6173 7365 7320 3d20  = 1;..classes = 
00000030: 7b0a 097d 3b0a                           {..};.

(see that archiveVersion is tab-indented, ascii 09)

What is being rebased:

(applied second, introduces the indention-problem)

$ git show 480cc3fff4b36f00f617277653517362f567aaf5:MyProject.xcodeproj/project.pbxproj | head -n 5 | xxd
00000000: 2f2f 2021 242a 5554 4638 2a24 210a 7b0a  // !$*UTF8*$!.{.
00000010: 0961 7263 6869 7665 5665 7273 696f 6e20  .archiveVersion 
00000020: 3d20 313b 0a09 636c 6173 7365 7320 3d20  = 1;..classes = 
00000030: 7b0a 097d 3b0a

(applied first)

$ git show ffafa60d714c94c7d7722e4f63aa08572f808f28:MyProject.xcodeproj/project.pbxproj | head -n 5 | xxd
00000000: 2f2f 2021 242a 5554 4638 2a24 210a 7b0a  // !$*UTF8*$!.{.
00000010: 0961 7263 6869 7665 5665 7273 696f 6e20  .archiveVersion 
00000020: 3d20 313b 0a09 636c 6173 7365 7320 3d20  = 1;..classes = 
00000030: 7b0a 097d 3b0a

See, all version contains ascii 09 and no spaces (ascii 20).

What could the problem be?

Here's the structure of the branches when rebasing:

As requested by someone:

$ git config --global apply.whitespace
$ git config apply.whitespace
$

(no output)