iBooks on Mavericks Beachballs Whenever Text Styling Occurs

Whenever I want to change text styling in iBooks the app becomes unresponsive. I kill it in the terminal (killall iBooks), and then the system reports that CoreText.FontDownloadHelper has crashed. My current theory is that if I'm to sort out CoreText.FontDownloadHelper, then the crash in iBooks won't occur any more. Am I right?

Here's the crash report, with the UUID removed.

Process:         CoreText.FontDownloadHelper [2865]
Path:            /System/Library/Frameworks/ApplicationServices.framework/Versions/A/Frameworks/ATS.framework/Versions/A/XPCServices/CoreText.FontDownloadHelper.xpc/Contents/MacOS/CoreText.FontDownloadHelper
Identifier:      CoreText.FontDownloadHelper
Version:         1.1 (1)
Code Type:       X86-64 (Native)
Parent Process:  launchd [398]
Responsible:     CoreText.FontDownloadHelper [2865]
User ID:         501

Date/Time:       2013-10-22 20:17:31.634 -0400
OS Version:      Mac OS X 10.9 (13A603)
Report Version:  11


Crashed Thread:  0  Dispatch queue: com.apple.main-thread

Exception Type:  EXC_BAD_INSTRUCTION (SIGILL)
Exception Codes: 0x0000000000000001, 0x0000000000000000

Application Specific Information:
Configuration error: Could not create listener. xpc_main() was probably called from a process that is not an XPC service bundle.

Thread 0 Crashed:: Dispatch queue: com.apple.main-thread
0   libxpc.dylib                    0x00007fff8d637b06 xpc_main + 359
1   com.apple.Foundation            0x00007fff8913d12b -[NSXPCListener resume] + 108
2   com.apple.CoreText.FontDownloadHelper 0x000000010a430f7b main + 106
3   libdyld.dylib                   0x00007fff91b045fd start + 1

Thread 1:
0   libsystem_kernel.dylib          0x00007fff87c4de6a __workq_kernreturn + 10
1   libsystem_pthread.dylib         0x00007fff87688f08 _pthread_wqthread + 330
2   libsystem_pthread.dylib         0x00007fff8768bfb9 start_wqthread + 13

Thread 2:: Dispatch queue: com.apple.libdispatch-manager
0   libsystem_kernel.dylib          0x00007fff87c4e662 kevent64 + 10
1   libdispatch.dylib               0x00007fff864e043d _dispatch_mgr_invoke + 239
2   libdispatch.dylib               0x00007fff864e0152 _dispatch_mgr_thread + 52

Thread 3:
0   libsystem_kernel.dylib          0x00007fff87c4de6a __workq_kernreturn + 10
1   libsystem_pthread.dylib         0x00007fff87688f08 _pthread_wqthread + 330
2   libsystem_pthread.dylib         0x00007fff8768bfb9 start_wqthread + 13

Thread 0 crashed with X86 Thread State (64-bit):
  rax: 0x00007fff8d642684  rbx: 0x00007f819950d620  rcx: 0x00000000000000ac  rdx: 0x0000000000000003
  rdi: 0x000000000000040b  rsi: 0x0000000010000003  rbp: 0x00007fff557d0bc0  rsp: 0x00007fff557d0b10
   r8: 0x0000000000000000   r9: 0x0000000000000000  r10: 0x00000000000000ac  r11: 0x0000000000000206
  r12: 0x000000010a468010  r13: 0x0000000000000000  r14: 0x00007fff8913d12b  r15: 0x0000000000000000
  rip: 0x00007fff8d637b06  rfl: 0x0000000000010206  cr2: 0x00007f8199402000

Logical CPU:     0
Error Code:      0x00000000
Trap Number:     6

I've managed to get rid of this problem by doing this:

1. open Font Book
2. run File > Restore Standard Fonts…

That basically moves all user-installed fonts to ~/Library/Fonts (Removed). So I suppose the problem is caused by one (or more) of the manually installed fonts.