Not sure if it's been noted yet, but SpriteFont 0.99.5RC in Construct build 0.99.5 crashes when you do anything (not sure if it's anything, but so far all the stuff I have tried) to it while its writing text. The only way around it is to include the "Is Writing" condition and invert it.
Perhaps I am just using it incorrectly? I love this plugin and it's obvious great work was put into it, so it might not be the plugin at all.