PDFtron close a tool before doing Frame.GoBack()

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Im using PDFtron <https://www.pdftron.com/> on a windows store app project.

I have a page with a back button and a pdf viewer where i can edit the pdfs.

When im editing a pdf i have a tool bar with options like the ones in the
samples, but i have a issue when i choose a Free Text tool and start
writing on the pdf, if i press the back button while the Free Text tool is
active ( the cursor is bliking) the text i wrote appears in the screen on
the next page i navigate to. (sometimes i get a crash).

How can i solve this?