As a
workaround you might try Shift-F8 which should be "Step out".
But there shouldn't be an asm window as result of doing F8.
Without a lot of details, it will be very hard to guess what may cause it.
f im using Zeos, and f8 enters to debug zeos units also.
Opening the source? Not the asm. So doing correct stepping? Just into code you don't want to step?
Also is that F8 "Step over" or F7 "Step into"?
F7 might step into Zeos, if Zeos is compiled with debug info.
Open the package, and look into the package's options. It has a debug page, like the project, and if that has debug info enabled, then "Step in" will go there.
Same if "Custom Options" has -gw or similar, or if it has "$(IDEBuildOptions)" and the IDE settings have -gw or similar.
Also, if it has (by any of those, or even other means) debug info, and it is compiled with -O2 or higher, then you may see really unexpected stepping.
Of course stepping can be interrupted by exceptions. Though then there should be a notification.
However, if an ignored exception (that is not shown by the debugger) is only caught in the caller of your current function, then that is like leaving the current function, and stepping will end. (in the finally/except block of the caller).
If it can't find the source for that, then that may open the asm window.
Otherwise, as for the asm Window, I am not sure what might cause it.
Please check what the "Stack Window", and report what the top 5 frames look like, when anything unexpected happens.
Is the function in which you started in the stack? At which position? And what is at the very top?
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Are there generics involved?