Well, ok, it seems two threads are stuck when this happens, from Process Hacker 2:
These threads both use 25% cpu/ 1 core.
TID 4780:
0, wow64cpu.dll!TurboDispatchJumpAddressEnd+0x6c0
1, wow64cpu.dll!TurboDispatchJumpAddressEnd+0x56b
2, wow64.dll!Wow64SystemServiceEx+0x1ce
3, wow64.dll!Wow64LdrpInitialize+0x42b
4, ntdll.dll!RtlUniform+0x6e6
5, ntdll.dll!RtlCreateTagHeap+0xa7
6, ntdll.dll!LdrInitializeThunk+0xe
7, ntdll.dll!NtDelayExecution+0x15
8, KernelBase.dll!Sleep+0xf
9, Open6022BE.exe!PrintdialogFinalize+0x3cc64
10, Open6022BE.exe!ConstantsFinalize+0x3352d
11, Open6022BE.exe!ConstantsFinalize+0x32400
12, Open6022BE.exe!MeasureFinalize+0x6dd27
13, Open6022BE.exe!MeasureFinalize+0x12e1e
14, user32.dll!gapfnScSendMessage+0x332
15, user32.dll!GetThreadDesktop+0xd7
16, user32.dll!CharPrevW+0x138
17, user32.dll!DispatchMessageW+0xf
18, Open6022BE.exe!MeasureFinalize+0x6e4cc
19, Open6022BE.exe!MeasureFinalize+0x6e50f
20, Open6022BE.exe!MeasureFinalize+0x6e83a
21, Open6022BE.exe!WaveformcolordialogFinalize+0x166
22, Open6022BE.exe!Tb2versioninitialization$qqrv+0x15197
23, kernel32.dll!BaseThreadInitThunk+0x12
24, ntdll.dll!RtlInitializeExceptionChain+0x63
25, ntdll.dll!RtlInitializeExceptionChain+0x36
0, KernelBase.dll!IsNLSDefinedString+0x476
1, 0x76548a4876523b6f
2, 0x7652449800000038
3, KernelBase.dll!IsNLSDefinedString+0x476
4, Open6022BE.exe!PrintdialogFinalize+0x3cc64
5, Open6022BE.exe!ConstantsFinalize+0x3352d
6, Open6022BE.exe!ConstantsFinalize+0x32400
7, Open6022BE.exe!MeasureFinalize+0x6dd27
8, Open6022BE.exe!MeasureFinalize+0x12e1e
9, user32.dll!gapfnScSendMessage+0x332
10, user32.dll!GetThreadDesktop+0xd7
11, user32.dll!CharPrevW+0x138
12, user32.dll!DispatchMessageW+0xf
13, Open6022BE.exe!MeasureFinalize+0x6e4cc
14, Open6022BE.exe!MeasureFinalize+0x6e50f
15, Open6022BE.exe!MeasureFinalize+0x6e83a
16, Open6022BE.exe!WaveformcolordialogFinalize+0x166
17, Open6022BE.exe!Tb2versioninitialization$qqrv+0x15197
18, kernel32.dll!BaseThreadInitThunk+0x12
19, ntdll.dll!RtlInitializeExceptionChain+0x63
20, ntdll.dll!RtlInitializeExceptionChain+0x36
0, ntdll.dll!NtDelayExecution+0x15
1, 0x76523bc877e3fd91
2, 0x18fb8800000000
3, 0xb6183fc9
4, 0x24f2c2000000003
5, 0x100000024
6, ntdll.dll!NtDelayExecution+0x15
7, KernelBase.dll!Sleep+0xf
8, Open6022BE.exe!PrintdialogFinalize+0x3cc64
9, Open6022BE.exe!ConstantsFinalize+0x3352d
10, Open6022BE.exe!ConstantsFinalize+0x32400
11, Open6022BE.exe!MeasureFinalize+0x6dd27
12, Open6022BE.exe!MeasureFinalize+0x12e1e
13, user32.dll!gapfnScSendMessage+0x332
14, user32.dll!GetThreadDesktop+0xd7
15, user32.dll!CharPrevW+0x138
16, user32.dll!DispatchMessageW+0xf
17, Open6022BE.exe!MeasureFinalize+0x6e4cc
18, Open6022BE.exe!MeasureFinalize+0x6e50f
19, Open6022BE.exe!MeasureFinalize+0x6e83a
20, Open6022BE.exe!WaveformcolordialogFinalize+0x166
21, Open6022BE.exe!Tb2versioninitialization$qqrv+0x15197
22, kernel32.dll!BaseThreadInitThunk+0x12
23, ntdll.dll!RtlInitializeExceptionChain+0x63
24, ntdll.dll!RtlInitializeExceptionChain+0x36
TID 2956:
0, wow64cpu.dll!TurboDispatchJumpAddressEnd+0x6c0
1, wow64cpu.dll!TurboDispatchJumpAddressEnd+0x56b
2, wow64.dll!Wow64SystemServiceEx+0x1ce
3, wow64.dll!Wow64LdrpInitialize+0x42b
4, ntdll.dll!RtlIsDosDeviceName_U+0x23a27
5, ntdll.dll!LdrInitializeThunk+0xe
6, ntdll.dll!NtDelayExecution+0x15
7, KernelBase.dll!Sleep+0xf
8, Open6022BE.exe!PrintdialogFinalize+0x3cc64
9, Open6022BE.exe!ScopeFinalize+0x31689
10, Open6022BE.exe!PrintdialogFinalize+0x3db30
11, Open6022BE.exe!DrawFinalize+0x310ae
12, Open6022BE.exe!MeasureFinalize+0x2dd06
13, kernel32.dll!BaseThreadInitThunk+0x12
14, ntdll.dll!RtlInitializeExceptionChain+0x63
15, ntdll.dll!RtlInitializeExceptionChain+0x36
0, wow64cpu.dll!CpuSimulate+0x16e
1, 0x42bff7400000000
2, 0x24f2c20007ffd8a
3, 0x7ffdf102541770
4, 0x80009802541770
5, 0x2541770007ffd60
6, 0x81263102583550
7, 0x81263b042bff58
8, 0x42bff7c042bff74
9, 0x42bff7400812691
10, ntdll.dll!NtDelayExecution+0x15
11, KernelBase.dll!Sleep+0xf
12, Open6022BE.exe!PrintdialogFinalize+0x3cc64
13, Open6022BE.exe!ScopeFinalize+0x31689
14, Open6022BE.exe!PrintdialogFinalize+0x3db30
15, Open6022BE.exe!DrawFinalize+0x310ae
16, Open6022BE.exe!MeasureFinalize+0x2dd06
17, kernel32.dll!BaseThreadInitThunk+0x12
18, ntdll.dll!RtlInitializeExceptionChain+0x63
19, ntdll.dll!RtlInitializeExceptionChain+0x36
0, KernelBase.dll!IsNLSDefinedString+0xca7
1, 0x76523bab042bfecc
2, 0x42bfea8
3, 0x6b22b3aa9
4, 0x24f2c2000000005
5, 0x100000024
6, KernelBase.dll!IsNLSDefinedString+0xca7
7, KernelBase.dll!SleepEx+0x48
8, KernelBase.dll!Sleep+0xf
9, Open6022BE.exe!PrintdialogFinalize+0x3cc64
10, Open6022BE.exe!ScopeFinalize+0x31689
11, Open6022BE.exe!PrintdialogFinalize+0x3db30
12, Open6022BE.exe!DrawFinalize+0x310ae
13, Open6022BE.exe!MeasureFinalize+0x2dd06
14, kernel32.dll!BaseThreadInitThunk+0x12
15, ntdll.dll!RtlInitializeExceptionChain+0x63
16, ntdll.dll!RtlInitializeExceptionChain+0x36