Inadvertent Whistle?

[rekent]

On one of those awful multi-purpose courts that is marked for every sport imaginable...

A1 is dribbling backwards and steps on a line near the division line that the T mistakes as actually being the division line. T blows his whistle, mechanically signals backcourt and verbalizes "Backco..." at which point he realizes his mistake and looks at L with a deer in the headlights look. They talk it over and T comes out, calls an inadvertent whistle and gives the ball back to A at the POI.

B coach goes crazy. "I officiated for X years, you can't do that!" Coach's rationale was that the mechanic had been given and official had begun verbalizing backcourt.

I know it is not a CE, but is an inadvertent whistle allowed here? Admittedly, I am rather weak in this area.