That wasn't "leaking stack memory" except in a very literal sense: the BASIC language keeps a stack of the control structures you're inside, so that when you hit an "End" or "Else" statement it knows where to go next. This "stack" of control structures isn't lexically scoped; it's dynamic, based on what control flow commands you've hit. So yes, if you use "Goto" to set up a situation where you're hitting "Then" over and over without ever hitting a corresponding "Else" or "End", the control flow stack will just keep getting deeper and deeper. That's not a "leak" per se: all those "Then" structures are still there, waiting for their "End"s, and will do the natural thing if you give their "End"s to them — even somewhere someone used to lexically scoped languages wouldn't expect. Sometimes you can do cool things with this.

See subsection 2.1 in https://www.ticalc.org/archives/files/fileinfo/145/14542.htm...

(I should add that the first image on that page shows one neat effect of non-lexicality: you can put an "Else" statement as the body of an "If", so that it's skipped when the "If"'s condition is false.)