The following script produces a "Tcl_Release couldn't find reference for 0x..." message followed by an "abnormal program termination" when Tcl exits:
package require XOTcl
set Interp [interp create] $Interp eval {package require XOTcl} interp delete $Interp
As you can see, XOTcl is being loaded once in the main interpreter and once in a sub-interpreter.
I'm running XOTcl 1.0.2 with Tcl 8.4.2 and 8.4.4 on Windows.