I tried TAB_SIZE = -1 (version 1.8.4 on windows) and got a crash (Doxyfile is further a standard Doxyfile). When trying my local version under cygwin I got:
Warning: argument `-1' for option TAB_SIZE is not a valid number in the range [1..16]!
Using the default: 4!

Program received signal SIGSEGV, Segmentation fault.
0x004211c7 in adjustConfiguration() ()
(gdb) where

+ Trace 232095

Source code:
/** @file aa.c
 * docu aa
 */


/** @brief docu fie
 */
void fie(void)
{
        int i;
}

(NOTE: before int i; is a <tab>)