[Serusers] SER crashed with DBG_QM_MALLOC on

[szj]

  I tested SER which have beed mofified by me.
The SER crahed with DBG_QM_MALLOC on, it report

 >qm_*: prev. fragm. tail overwritten(c0003433, 
abcdefed)[0x814f284:0x814f29c]!
this happened in one of my function which called pkg_malloc().
this function is located in the tm module.

  But if comment the DBG_QM_MALLOC in the
Makefile.defs , then compile SER, it never
crashes.
  Who can tell me what that mean??
  Thanks for your help.

 Best Regards.
 Sun Zongjun