I assume this is when you press F8 (step over)?
And I assume your fpc is the default install that came with Lazarus?
And you are using the default debugger?
There is a known issue between Fpc and Gdb (don't know which one causes the bug) that can lead to such "step in" where not expected.
Menu: Tools > Option: page Debugger > General (or in svn trunk: backend)
There is a property grid. In it is an option "FixIncorrectStepOver" -> set it to true.
There also is a checkbox "Auto close asm window" => which means, if the asm window opens, and you do "step over", "step out" (back to your code), then the asm window gets closed again.
Alternatively search the forum/wiki for fpdebug / LazDebuggerFp and install/configure this.