'g' appearing after each return

When used interactively, gst shows 'g' after each return.

Example (| = caret position):

prompt>'Hello, World' printNl !|<return>

results in:

prompt>'Hello, World' printNl !
g|

the statement doesn't even get evaluated. I need to press return again for the result to appear, and it appears twice. It doesn't happen if it executes the statements from a file.

Platform: i386-mingw32