I'm running Oracle 8.0.5 (production) with PHP3 latest CVS and Apache 1.3.3. To reproduce the crash:
- run a script with Ora_Plogon
- stop oracle
- reload the script, apache core dumps.

Here is the dump:

(gdb) back
#0  0x404a9954 in   ()
#1  0x820ecd0 in ?? ()
#2  0x401610c4 in ntpwr ()
#3  0x40152b06 in nspsend ()
#4  0x4014623d in nsdofls ()
#5  0x40145407 in nsdo ()
#6  0x4012225f in nioqrc ()
#7  0x4021a7a1 in ttcdrv (context=0x8201708 "\004", opts=0) at ttcdrv.c:487
#8  0x40127a2d in nioqwa ()
#9  0x4010386c in upirtrc ()
#10 0x40103492 in upirtr ()
#11 0x400f9bde in upiopn ()
#12 0x400f435b in ociope ()
#13 0x4010f0dd in oopen ()
#14 0x8090b74 in _ora_ping (conn=0x81ded50) at functions/oracle.c:347
#15 0x8090f90 in php3_Ora_Do_Logon (ht=0x82078b0, return_value=0x8121eb0, 
    list=0x8123e08, plist=0x8123ddc, persistent=1) at functions/oracle.c:511
#16 0x8090c1b in php3_Ora_PLogon (ht=0x82078b0, return_value=0x8121eb0, 
    list=0x8123e08, plist=0x8123ddc) at functions/oracle.c:373


I tried to narrow down the problem and wrote a small OCI programm to reproduce the problem, but it works fine. The programm connects to Oracle, stops (so you can shut down oracle). Then it tries to open a new cursor, it fails but it does not core dump.