Editing qtc_packaging/debian_*/rules changes tabs to spaces

Steps to reproduce

1. Update Qt SDK to include experimental Harmattan support.
2. Check out http://gitorious.org/attitude/attitude
3. Double click on _Projects > Attitude > Other files > qtc_packaging > debian_harmattan > rules
4. Try to add a set command in configure-stamp, as it's a shell command in a Makefile, it needs to be preceded by a tab character.

Expected outcome

1. Pressing "tab" in a Makefile (such as debian/rules) will insert a tab character, not multiple spaces.
2. Pasting a tab character from another line and saving the file maintains the newly pasted tab.

Actual outcome

Tab inserts the number of configured characters. Pasting a tab seems to work, but when the file is saved it's converted into spaces (other tabs in the file are unaffected)