Here is a paragraph that I copied from a TI spec
on " LM7805MP/NOPB " regulators. Could this be whats happening
with the 5 Volt regulator, the center pin of the power
connector is making before the ground side thus causing
the full supply voltage to be present on the output of
the 5 volt regulator>
" 8.1.3 Regulator Floating Ground
When the ground pin alone becomes disconnected, the output approaches the unregulated input, causing possible damage to other circuits connected to VOUT. If ground is reconnected with power ON, damage may also occur to the regulator. This fault is most likely to occur when plugging in regulators or modules with on card regulators into powered up sockets. The power must be turned off first, the thermal limit ceases operating, or the ground must be connected first if power must be left on. See Figure 16."