Default HELP, Weird charging Issue

HI All,
I just unlocked bootloader, rooted, S-OFF, and installed custom recovery TWRP 2710 GSM, on stock ROM.
All went well.
However, everytime I connect to charger whilst phone is on OFF mode, it starts the TWRP recovery screen for few seconds, then disappears.
when I short press the power button, it shows recovery background. is this OK?
anyone knows what is wrong? thanks in advance.