If php_COM_invoke receives an error as a result of trying to invoke a COM method via C_TYPEINFO_VT(obj)->Invoke, it assumes that the dispatch failed and tries again using C_DISPATCH_VT(obj)->Invoke.

However, if the first Invoke succeeds (i.e. actually call into the object method) but the method raises a COM exception, it returns DISP_E_EXCEPTION.  php_COM_invoke will then call the same method again using C_DISPATCH_VT.

(In my particular case, the COM method was performing some subsequent phases of a larger DB transaction, encountered a deadlock, then rolled back the DB transaction and reported the event by raising an exception.  php_COM_invoke swallowed the exception without report and invoked the method again, which, this time, did not encounter the same deadlock, leaving my code without knowledge that a deadlock had caused some of my DB updates to be rolled back.  It took me four days to figure out what in the world was happening.)

Here's a diff against COM.c which checks for DISP_E_EXCEPTION as a special case.  (This diff is against 4.3.2RC1 but AFAICS this error has existed all along.)

diff -r temp/php-4.3.2RC1\ext\com\COM.c php-4.3.2RC1\ext\com\COM.c
128,129c128,130
< 				hr = C_DISPATCH_VT(obj)->Invoke(C_DISPATCH(obj), dispIdMember, &IID_NULL, LOCALE_SYSTEM_DEFAULT, wFlags, pDispParams, pVarResult, &ExceptInfo, &ArgErr);
< 				if (SUCCEEDED(hr)) {
---
> 				if(hr != DISP_E_EXCEPTION) {
> 					hr = C_DISPATCH_VT(obj)->Invoke(C_DISPATCH(obj), dispIdMember, &IID_NULL, LOCALE_SYSTEM_DEFAULT, wFlags, pDispParams, pVarResult, &ExceptInfo, &ArgErr);
> 					if (SUCCEEDED(hr)) {
131,137c132,139
< 					 * ITypLib doesn't work
< 					 * Release ITypeLib and fall back to IDispatch
< 					 */
< 
< 					C_TYPEINFO_VT(obj)->Release(C_TYPEINFO(obj));
< 					C_HASTLIB(obj) = FALSE;
< 					C_TYPEINFO(obj) = NULL;
---
> 					* ITypLib doesn't work
> 					* Release ITypeLib and fall back to IDispatch
> 						*/
> 						
> 						C_TYPEINFO_VT(obj)->Release(C_TYPEINFO(obj));
> 						C_HASTLIB(obj) = FALSE;
> 						C_TYPEINFO(obj) = NULL;
> 					}