rcx syscall return address not transparent when xl8 app state

I observed in burst_threadfilter test that when a thread is occasionally suspended at syscall, the xcx value is not getting restored.

Code cache:

0x00005633d5cf8c40 0f 05 syscall -> %rcx

Looping on synch with thread 14524 recreate_app_state -- translating from: priv_mcontext_t @0x00007fcb68d12780 xax = 0x00000000000000ca xbx = 0x00007fcb6ad17700 xcx = 0x00005633d5cf8c42 xdx = 0x00000000000038bd xsi = 0x0000000000000000 xdi = 0x00007fcb6ad179d0 xbp = 0x0000000000000000 xsp = 0x00007ffeb3574190 r8 = 0x00000000000000ca r9 = 0x00007fcb6ad179d0 r10 = 0x0000000000000000 r11 = 0x0000000000000246 r12 = 0x0000000000000000 r13 = 0x00007ffeb35741a0 r14 = 0x0000000000000000 r15 = 0x0000000000000000 ymm0= 0x0000000000000000000000000000000000000000000000000000000000000000 ymm1= 0x6b10456000007fcb6b107bc000007fcb00000000000000000000000000000000 ymm2= 0x66666f2d656e696c616d2d2072745f7800000000000000000000000000000000 ymm3= 0x6474732d5f7272656b73616d6378302000000000000000000000000000000000 ymm4= 0xb357539300007ffeb35753a900007ffe00000000000000000000000000000000 ymm5= 0xb3575f4700007ffeb3575f6700007ffe00000000000000000000000000000000 ymm6= 0xb3575e4900007ffeb3575e7600007ffe00000000000000000000000000000000 ymm7= 0xb3575dba00007ffeb3575dcb00007ffe00000000000000000000000000000000 ymm8= 0xb3575d6500007ffeb3575d7400007ffe00000000000000000000000000000000 ymm9= 0x0000000000000000000000000000000000000000000000000000000000000000 ymm10= 0x0000000000000000000000000000000000000000000000000000000000000000 ymm11= 0x0000000000000000000000000000000000000000000000000000000000000000 ymm12= 0x0000000000000000000000000000000000000000000000000000000000000000 ymm13= 0x0000000000000000000000000000000000000000000000000000000000000000 ymm14= 0x0000000000000000000000000000000000000000000000000000000000000000 ymm15= 0x0000000000000000000000000000000000000000000000000000000000000000 mxcsr=0x00001fa0 eflags = 0x0000000000000246 pc = 0x00005633d5cf8c40 recreate_app pc = after_syscall, translating recreate_app_state -- translation is: priv_mcontext_t @0x00007fcb68d12780 xax = 0x00000000000000ca xbx = 0x00007fcb6ad17700 xcx = 0x00005633d5cf8c42 xdx = 0x00000000000038bd xsi = 0x0000000000000000 xdi = 0x00007fcb6ad179d0 xbp = 0x0000000000000000 xsp = 0x00007ffeb3574190 r8 = 0x00000000000000ca r9 = 0x00007fcb6ad179d0 r10 = 0x0000000000000000 r11 = 0x0000000000000246 r12 = 0x0000000000000000 r13 = 0x00007ffeb35741a0 r14 = 0x0000000000000000 r15 = 0x0000000000000000 ymm0= 0x0000000000000000000000000000000000000000000000000000000000000000 ymm1= 0x6b10456000007fcb6b107bc000007fcb00000000000000000000000000000000 ymm2= 0x66666f2d656e696c616d2d2072745f7800000000000000000000000000000000 ymm3= 0x6474732d5f7272656b73616d6378302000000000000000000000000000000000 ymm4= 0xb357539300007ffeb35753a900007ffe00000000000000000000000000000000 ymm5= 0xb3575f4700007ffeb3575f6700007ffe00000000000000000000000000000000 ymm6= 0xb3575e4900007ffeb3575e7600007ffe00000000000000000000000000000000 ymm7= 0xb3575dba00007ffeb3575dcb00007ffe00000000000000000000000000000000 ymm8= 0xb3575d6500007ffeb3575d7400007ffe00000000000000000000000000000000 ymm9= 0x0000000000000000000000000000000000000000000000000000000000000000 ymm10= 0x0000000000000000000000000000000000000000000000000000000000000000 ymm11= 0x0000000000000000000000000000000000000000000000000000000000000000 ymm12= 0x0000000000000000000000000000000000000000000000000000000000000000 ymm13= 0x0000000000000000000000000000000000000000000000000000000000000000 ymm14= 0x0000000000000000000000000000000000000000000000000000000000000000 ymm15= 0x0000000000000000000000000000000000000000000000000000000000000000 mxcsr=0x00001fa0 eflags = 0x0000000000000246 pc = 0x00007fcb6bc54d2b

xcx is still code cache return address. I have seen the same thread crashing but it is likely crashing because of some other issue.