SUMMARY

When you try to change the voice for tts after having it speak at least once and have it speak again in a different voice, okular will segfault.

Attaching the dump from address sanitizer:
AddressSanitizer:DEADLYSIGNAL
=================================================================
==210696==ERROR: AddressSanitizer: SEGV on unknown address 0x000000043e93 (pc 0x7fac9b0c3a51 bp 0x7fac9b47a1ab sp 0x7fac9bca05d0 T27)
==210696==The signal is caused by a READ memory access.
    #0 0x7fac9b0c3a51 in feat_set (/usr/lib/qt6/plugins/texttospeech/../../../libflite.so.1+0x15a51) (BuildId: 0e2a7bfdf452f147252174342fe4ecba0025d90d)
    #1 0x7fac9b47499b  (/usr/lib/qt6/plugins/texttospeech/libqtexttospeech_flite.so+0xb99b) (BuildId: 29e2c9357edb2c021b1994addcc167a73d58d4a3)
    #2 0x7faccee542c6 in QObject::event(QEvent*) (/usr/lib/libQt6Core.so.6+0x17c2c6) (BuildId: b7de086c703c3347ad87118effe4f0429fb6fef8)
    #3 0x7faccfe5238a in QApplicationPrivate::notify_helper(QObject*, QEvent*) (/usr/lib/libQt6Widgets.so.6+0xf438a) (BuildId: 9042b7a7402bce90a3c5ef04990d5ad1adafe229)
    #4 0x7faccee11817 in QCoreApplication::notifyInternal2(QObject*, QEvent*) (/usr/lib/libQt6Core.so.6+0x139817) (BuildId: b7de086c703c3347ad87118effe4f0429fb6fef8)
    #5 0x7faccee11b9a in QCoreApplicationPrivate::sendPostedEvents(QObject*, int, QThreadData*) (/usr/lib/libQt6Core.so.6+0x139b9a) (BuildId: b7de086c703c3347ad87118effe4f0429fb6fef8)
    #6 0x7faccf04d8a3  (/usr/lib/libQt6Core.so.6+0x3758a3) (BuildId: b7de086c703c3347ad87118effe4f0429fb6fef8)
    #7 0x7faccd584f68  (/usr/lib/libglib-2.0.so.0+0x59f68) (BuildId: adcf94ff81298387baa7b55fa88c9ba80b3283a6)
    #8 0x7faccd5e33a6  (/usr/lib/libglib-2.0.so.0+0xb83a6) (BuildId: adcf94ff81298387baa7b55fa88c9ba80b3283a6)
    #9 0x7faccd583161 in g_main_context_iteration (/usr/lib/libglib-2.0.so.0+0x58161) (BuildId: adcf94ff81298387baa7b55fa88c9ba80b3283a6)
    #10 0x7faccf04b9c3 in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) (/usr/lib/libQt6Core.so.6+0x3739c3) (BuildId: b7de086c703c3347ad87118effe4f0429fb6fef8)
    #11 0x7faccee1bd6d in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) (/usr/lib/libQt6Core.so.6+0x143d6d) (BuildId: b7de086c703c3347ad87118effe4f0429fb6fef8)
    #12 0x7facceef916e in QThread::run() (/usr/lib/libQt6Core.so.6+0x22116e) (BuildId: b7de086c703c3347ad87118effe4f0429fb6fef8)
    #13 0x7faccef78bd2  (/usr/lib/libQt6Core.so.6+0x2a0bd2) (BuildId: b7de086c703c3347ad87118effe4f0429fb6fef8)
    #14 0x7facce7a8559  (/usr/lib/libc.so.6+0x8f559) (BuildId: 0865c4b9ba13e0094e8b45b78dfc7a2971f536d2)
    #15 0x7facce825a3b  (/usr/lib/libc.so.6+0x10ca3b) (BuildId: 0865c4b9ba13e0094e8b45b78dfc7a2971f536d2)

AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV (/usr/lib/qt6/plugins/texttospeech/../../../libflite.so.1+0x15a51) (BuildId: 0e2a7bfdf452f147252174342fe4ecba0025d90d) in feat_set
Thread T27 (QThread) created by T0 here:
    #0 0x7facd1740497 in __interceptor_pthread_create /usr/src/debug/gcc/gcc/libsanitizer/asan/asan_interceptors.cpp:208
    #1 0x7faccef7bf96 in QThread::start(QThread::Priority) (/usr/lib/libQt6Core.so.6+0x2a3f96) (BuildId: b7de086c703c3347ad87118effe4f0429fb6fef8)

==210696==ABORTING


STEPS TO REPRODUCE
1.  Have some text spoken. You can do it either with selection, or speak current page or any other alternative.
2.  In Configure Okular << Accessibility, change the voice. My testing was done with flite and the voices I had were slt and kal16.
3. Have text spoken again. Okular will crash with a segfault.

OBSERVED RESULT
Segfault.

EXPECTED RESULT
The text should be spoken with changed voice.

SOFTWARE/OS VERSIONS
Linux: Manjaro (unstable branch)
(available in About System)
DE used : XFCE
KDE Frameworks Version: 6.0.0
Qt Version: 6.6.2

ADDITIONAL INFORMATION
I tried debugging around a bit in the Okular source, but no values seem to be going null. Could be an issue with the qt texttospeech plugin?