What version of Go are you using (go version)?

go version go1.15 windows/amd64

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

set GO111MODULE=
set GOARCH=amd64
set GOBIN=
set GOCACHE=C:\Users\Hamza\AppData\Local\go-build
set GOENV=C:\Users\Hamza\AppData\Roaming\go\env  
set GOEXE=.exe
set GOFLAGS=
set GOHOSTARCH=amd64
set GOHOSTOS=windows
set GOINSECURE=
set GOMODCACHE=C:\Users\Hamza\go\pkg\mod
set GONOPROXY=
set GONOSUMDB=
set GOOS=windows
set GOPATH=C:\Users\Hamza\go
set GOPRIVATE=
set GOPROXY=https://proxy.golang.org,direct
set GOROOT=c:\go
set GOSUMDB=sum.golang.org
set GOTMPDIR=
set GOTOOLDIR=c:\go\pkg\tool\windows_amd64
set GCCGO=gccgo
set AR=ar
set CC=gcc
set CXX=g++
set CGO_ENABLED=1
set GOMOD=D:\Projects\tools\go.mod
set CGO_CFLAGS=-g -O2
set CGO_CPPFLAGS=
set CGO_CXXFLAGS=-g -O2
set CGO_FFLAGS=-g -O2
set CGO_LDFLAGS=-g -O2
set PKG_CONFIG=pkg-config
set GOGCCFLAGS=-m64 -mthreads -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=R:\Temp\go-build900148230=/tmp/go-build -gno-record-gcc-switches

What did you do?

Given the following .slide file

Let's break stuff

* Time to break
.play -edit break.go

And the following go file

package main

import (
	"fmt" // this is a comment
)

func main() {
	fmt.Println("Hello world!")
}

Running go present and navigating to the second slide with the editable code.

Importing time in the slide while presenting like so

package main

import (
	"fmt" // this is a comment
        "time"
)

func main() {
	fmt.Println("Hello world!")
}

And then running the code.

What did you expect to see?

There should be an error because time is not in use.

What did you see instead?

It still shows the Hello world! output.

Further explanation (with pics)

I investigated this further and it looks like the issue is on the html side.

Here's how the html looks like initially

Pressing enter in the slide code adds another <pre> tag that essentially splits the code

Typing "time" doesn't add a new span for it

This results in "time" getting interpreted as being on the same line as the comment (// this is a comment).
Therefore, the snippet complies and runs.